CHAPTER
14 QUANTIATIVE RISK ASSESSMENT (Đánh giá rủi ro định lượng)
The purpose of this chapter is to provide an understanding of risk, how to assess it at a specific site, and what the numerical estimates of risk represent The !ational Research Council defines risk assessment as (mục đích của chương này là cung cấp sự hiểu i!" #$ sự rủi ro% đánh giá n& như "h! nào "'i m" hu #ực hi*n "rư+ng cụ "hể% #à các "ính "oán s, h-c của sự rủi ro iểu "hị cho cái g./ 0i đ1ng nghi2n c3u hoa h-c 4u,c gia định ngh5a 6đánh giá rủi ro7 như sau )8 )8
" the charac character teri#a i#atio tionn of the potent potential ial advers adversee health health effect effectss of hum human an e$posu e$posures res to enviro environme nmenta ntall ha#ards"Risk assessment also includes characteri#ation of the uncertainties inherent in the process of inferring risk (9là sự m: "; đ;y ra đ!n con ngư+i #à nguy hiểm cho m:i "rư+ng9 Đánh giá rủi ro c?ng ao g1m sự m: "; đ
Risk assessment is a tool for understanding the health and environmental ha#ards associated with ha#ardous waste and can greatl% improve the &asis on which to make ha#ardous waste management decisions Risk assessment can also assist the pu&lic in understanding the human health implications of the issues and availa&le alternatives (đánh giá rủi ro là m" c:ng cụ để hiểu #$ các nguy cơ c& h'i cho m:i "rư+ng #à s3c hAB Co chấ" "h;i nguy h'i gDy n2n #à c& "hể "Eng cư+ng n$n ";ng cho #i*c đưa ra nhFng 4uy!" sách 4u;n lG chấ" "h;i nguy h'i/ Đánh giá rủi ro c?ng c& "hể giHp đI cng đ1ng hiểu #$ các #ấn đ$ li2n 4uan mJ" "hi!" đ!n s3c hAB con ngư+i #à các phương án sKn c&/)/
14-1 RISK (rủi ro)
'n the classical sense, risk is defined as the as the pro&a&ilit% of suffering harm or loss (hen the resulting harm is measura&le )eg, worker*da%s lost to accidents+, risk ma% &e calculated as the pro&a&ilit% of an action occurring occurring multiplied multiplied &% the severit% of the harm if the action does occur ("hBo G ngh5a c@ điển% rủi ro được định ngh5a như là h; nEng >;y ra sự mấ" má" hay sự gDy h'i/ Lhi !" 4u; gDy h'i này c& "hể đo lư+ng được (#í Cụ% ngày c:ng ị mấ" Co "ai n'n))% "h. sự rủi ro này c& "hể được "ính như là >ác suấ" của m" hành đng >;y ra nhDn #Mi m3c đ nghi2m "r-ng của sự gDy h'i đ& n!u hành đng đ& >;y ra)
Risk - )pro&a&ilit%+ $ )severit% of conse.uence+ R/i ro - )$0c sut+ $ )m2c 3 nghi5m tr6ng c/a k7t .u8+ (Ni*c sO Cụng Cụ ng phPp "ính 9sing this calculation suggests that the following two t wo activities have the same risk (Ni*c này đưa ra Q hành đng c& cRng rủi ro như sau) Activity no.
Severity of outcome, worer-!"y# $o#t
%ro&"&i$ity of outcome
Ri#, worer!"y# $o#t
1
:;
;1
:
:
1;
;:
:
or such conse.uences, risk is simpl% defines as the pro&a&ilit% of the harm occurring ?ecause appro$imatel% :@ percent of the 9 population will e$perience cancer in their lifetime, the lifetime lifeti me risk is &ackground, incremental, or total risk '"c(roun! ri# is is what people are e$posed to in the a&sence of the particular source of risk &eing studied, increment"$ ri# is is that caused &% this source, and total risk is simpl% the sum of the two The previous reference to ;:@ pro&a&ilit% of cancer represents &ackground risk The 9 Environmental Protection Agenc% )EPA+ target for uperfund sites of 1$1; *B e$cess lifetime cancer risk represents an incremental risk the pro&a&ilit% of a person developing cancer from e$posure to contaminants from a uperfund site is 1$1;*B )or Done in a million+ in e$cess e$cess of that personFs personFs risk of cancer from all other sources sources com&ined com&ined 't also implies that for ever% million million people potential e$posed e$posed to a site, one additional additional cancer case over their lifetimes would &e e$pected 'f the population e$posed to a site is 1;,;;;, this num&er can &e interpreted as ;;1 additional occurrence of cancer (Sác !" 4u; h:ng mong mu,n "hư+ng h:ng ph;i là #ấn đ$ c& "hể >ác định s, lượng/ T" #í Cụ của !" 4u; này là cái ch!"U h:ng c& ai ao gi+ là hơi ch!"/ T" #í Cụ hác là sự >Dm nhJp của *nh ung "hư/ NMi nhFng !" 4u; như #Jy% rủi ro được định ngh5a đơn gi;n là >ác suấ" >;y ra sự "@n h'i/ V=i #. ho;ng QWX CDn s, 0oa LY sZ "r;i 4ua *nh ung "hư "rong cuc đ+i h-% sự rủi ro "rong cuc đ+i là sự rủi ro n$n% rủi ro gia "Eng hay rủi ro "oàn / / Rủi Rủi ro nền là nền là nhFng g. mà con ngư+i "i!p >Hc "rong đi$u i*n h:ng c& ngu1n phá" sinh rủi ro đác suấ" của *nh ung "hư đ'i Ci*n cho rủi ro n$n/ Sh] "i2u của Sơ 4uan V;o #* T:i "rư+ng 0oa LY cho các địa điểm [upBr^unC nguy cơ ung "hư là #ượ" 4uá _>_\` đ'i Ci*n cho rủi ro gia "Eng b >ác suấ" của m" ngư+i phá" "riển ung "hư Co phơi nhim các chấ" đc "d m" địa điểm [upBr^unC là _>_\` (hay 6m" phen m" "ri*u7) #ượ" 4uá nguy cơ ung "hư "d các ngu1n hác !" hợp l'i của ngư+i đ&/ f& c?ng hàm G rng mi m" "ri*u ngư+i "i!p >Hc #Mi địa điểm này% "h. sZ c& "hể c & m" ngư+i mc "h2m *nh ung "hư "rong cuc đ+i của c ủa h-/ f!u c& _\%\\\ ngư+i "i!p >Hc #Mi m" địa điểm% "h. s, này c& "hể được "hể hi*n như là "h2m \/\_ h; nEng mc *nh ung "hư )
Ta&le 14*1 provides some estimates of some common place risks )death in the case of accidents and cancer for the other actions+ These present &ackground risks on an annual &asis (V;ng _j`_ cung cấp m" #ài ưMc "ính rủi ro cho m" #ài nơi ph@ i!n (ch!" "rong "rư+ng hợp "ai n'n #à ung "hư Co các ho'" đng hác)/ fhFng cái này "r.nh ày #$ nhFng rủi ro n$n "r2n m" n$n ";ng cơ ;n "h:ng "hư+ng)/
The terms risk and ha#ard are often confused )"*"r! is a descriptive term, referring to the intrinsic capa&ilit% of the waste to cause harm= it is the source of the risk The ha#ard posed &% a waste is a function of such varia&les as its to$icit%, mo&ilit%, and persistence as well as how it is contained The release or threatened release of a ha#ardous waste thus represents a ha#ard it is a source of risk= however, the waste does not represent a risk unless e$posure has occurred or the possi&ilit% e$ists for future e$posure ("huJ" ngF rủi ro (ris) #à nguy h'i (hakarC) "hư+ng hay ị ln ln #Mi nhau/ Hazard nhau/ Hazard là là m" "huJ" ngF m: ";% đ$ cJp đ!n h; nEng ni "'i của chấ" "h;i gDy ra sự "hi*" h'i hay "@n h'iU n& là ngu1n g,c sinh ra rủi ro/ [ự nguy h'i gDy ra =i chấ" "h;i là các "ính chấ" đc h'i% "ính C i!n đ@i #à sự lưu l'i lDu Cài của n& cRng #Mi #i*c n& được ch3a đựng như "h! nào/ N. #Jy% #i*c phá" "h;i hay sự gi;i ph&ng mang "ính đB C-a của chấ" "h;i đc h'i đ'i Ci*n cho sự nguy h'i b n& là ngu1n g,c của rủi roU "uy nhi2n% chấ" "h;i đ& h:ng đ'i Ci*n cho rủi ro "rd hi >;y ra sự phơi nhim nh im houấ" hi* hi*nn sự phơi nhim "rong "ương lai) lai) TA'+E 14-1 ommon ri## (các rủi ro ph@ i!n) Annu"$ Ri# (rủi
Uncert"inty ("ính h:ng
ro hang nEm)
@n định)
Total ("@ng)
:4 $ 1;*4
1;L
Pedestrian (ngư+i đi )
4: $ 1;*@
1;L
Home accidents ("ai n'n = nhà)
11 $ 1;*4
@L
Cigarette smoking )one pack per da%+ (hH" "hu,c lá
IB$ 1;*I
>actor of I
J $ 1;*B
>actor of I
: $ 1;*K
>actor of 1;
Action (ho'" đng)
Gotor vehicle accident ("ai n'n >B máy)
_ g&i mi ngày)
Peanut &utter )4 teaspoon per da%+ (ơ l'c j mung mi ngày)
rinking water with EPA limit of TCE (u,ng nưMc c& chấ" đc S (richloroB"hylBnB) (richloroB"hylBnB) nm "rong giMi
h'n của )
Emer(ency "# " Sy#tem"tic Meto!o$o(y ("rong "rư+ng hợp hqn cấp như là m" phương pháp c& h* "h,ng)
9ndou&tedl%, the concept of risk has a long histor% of influencing environmental polic% making However, the initial efforts relied more on intuition than on the scientific principles of to$icolog%, chemistr%, and fate and transport modeling inherent in modern risk assessments
'n this chapter we will use the term 4uan"i"a"i#B to descri&e the process of using scientific principles to calculate .uantitative estimates of risk The widel% recogni#ed approach is a four*stage process (rong chương này% chHng "a sZ sO Cụng "huJ" ngF định lượng (4uan"i"a"i#B) để m: "; 4uá "r.nh sO Cụng các nguy2n lG hoa h-c để ưMc "ính định lượng rủi ro) 1.
Ha#ard identification )which chemicals are important+ (nhJn C'ng m,i nguy h'i (chấ" h&a h-c nào là 4uan "r-ng))
2.
E$posure assessment )where the chemicals go, who might &e e$posed and how+ (đánh giá sự phơi nhim (các chấ" h&a h-c đi đ!n đDu% nhFng ai sZ c& "hể ị phơi nhim #à như "h! nào))
3.
To$icit% assessment )determining numerical indices of to$icit% for computing risk+ (đánh giá đc "ính (>ác định các ch] s, s, h-c của đc "ính để "ính "oán rủi ro))
4.
Risk characteri#ation )estimating the magnitude of risk, and the uncertaint% of the estimate+ (m: "; đ
Risk assessment, as performed under most ha#ardous waste regulator% programs, emplo%s this concept of conducting the risk assessment process in these four*stage The 9 !ational Academ% of ciences created the four*stage process and eventuall% the EPA codified it The EPA first applied the concept in 1KJ4 for carcinogens following a suit &rought &% the !atural Resources efense Council regarding am&ient water .ualit% criteria 'n response to this suit, the EPA issued slope factors )>s+ that could &e utili#ed in a predictive capacit% to estimate carcinogenic risk to potentiall% e$posed populations A similar approach was then applied to non*carcinogens &% setting accepta&le dail% intake )A'+ levels, which are analogous to reference concentrations )RfCs+ 't should &e noted that although >s have also &een named &% various acron%ms including C>)carcinogenic slope factor+ and CP> )carcinogenic potenc% factor+, all t erms refer to e$pected lifetime cancer risk if someone is e$posed dail% for N; %ears to 1mg of su&stance per kilogram &od% weight (đánh giá rủi ro% được "hực hi*n "rong heu h!" các chương "r.nh đi$u "i!" chấ" "h;i nguy h'i% sO Cụng hái ni*m này để "i!n hành các 4uy "r.nh đánh giá rủi ro "rong j giai đo'n/ Sơ 4uan Lhoa h-c vu,c gia 0oa LY đt "'o ra 4ui "r.nh j giai đo'n này #à cu,i cRng là đt h* "h,ng h&a n&/ đt áp Cụng hái ni*m này len đeu "i2n nEm _wxj #Mi chấ" gDy ung "hư sau m" #ụ i*n được "i!n hành =i 0i đ1ng ;o #* ài nguy2n vu,c gia li2n 4uan đ!n #ấn đ$ chấ" lượng nưMc >ung 4uanh/ Để đ,i ph& #Mi #ấn đ$ này% đt an hành các h* s, C,c ([s) cái mà c& "hể được sO Cụng "rong h; nEng Cự đoán để ưMc "ính rủi ro của chấ" gDy ung "hư đ!n lượng CDn cư c& h; nEng đt "i!p >Hc #Mi n&/ T" cách "i!p cJn "ương "ự đt được áp Cụng sau đ& cho các chấ" h:ng gDy ung "hư ng cách "hi!" lJp các m3c đ "i2u "hụ hàng ngày (z{) c& "hể chấp nhJn được% n& "ương "ự như là các n1ng đ "ham chi!u (^Ss)/ f2n nhM rng% mHc hàng ngày "rong |\ nEm "Mi _mg #J" chấ" cho mi g "r-ng lượng cơ "hể)
%uro#e# of Ri# A##e##ment (Sác mục đích của #i*c đánh giá rủi ro)
9sing the estimates calculated &% a risk assessment as a &asis for making decisions is termed risk management Ri# m"n"(ement ma% &e defines as (Ni*c sO Cụng các ưMc "ính đt được "ính "oán =i sự đánh giá rủi ro như là n2n ";ng cho các 4uy!" sách được g-i là 4u;n lG rủi ro)/Quản lý rủi ro c& "hể định ngh5a như sau
"evaluating alternative"actions and selecting among them"entails consideration of political, social, economic, and engineering information with risk*related information to develop, anal%#e, and compare regulator% options and to select the appropriate regulator% response to a potential chronic health ha#ard The selection process necessaril% re.uires the use of value Mudgments on such issues as the accepta&ilit% of risk and the reasona&leness of the costs of control (9đánh giá lựa ch-n9các ho'" đng #à lựa ch-n "rong s, chHng9đi hAi sự 4uan "Dm của các "h:ng "in chính 4uy$n% >t hi% inh "!% #à } "huJ" #Mi các "h:ng "in li2n 4uan đ!n rủi ro để phá" "riển% phDn "ích #à so sánh các "Ry ch-n đi$u "i!" #à ch-n lựa ra các chính sách đi$u "i!" phR hợp ph;n 3ng l'i #Mi m,i nguy h'i c& h; nEng >;y ra "hư+ng >uy2n đ!n s3c hAB)
'n the ha#ardous waste field, risk assessment provides information to decision makers as to the conse.uences of possi&le actions 'mportant decisions that could use risk estimates include selecting waste treatmentO disposal options, remediating contaminated sites, minimi#ing waste generation, sitting new facilities, and developing new products 't should &e emphasi#ed that risk estimates are onl% one t%pe of information used, and ha#ardous waste decisions are often driven &% political, social, economic, or other factors ("rong l5nh #ực chấ" "h;i nguy h'i% đánh giá rủi ro cung cấp "h:ng "in cho các nhà ho'ch định chính sách như là !" 4u; của các ho'" đng c& "hể >;y ra/ Sác 4uy!" định 4uan "r-ng mà c& "hể sO Cụng các ưMc "ính rủi ro ao g1m #i*c lựa ch-n các phương án >O lG~ "h;i A chấ" "h;i% "qy u! các địa điểm ị : nhim chấ" đc% gi;m "hiểu sự phá" sinh chấ" "h;i% lự a ch-n địa điểm >Dy Cựng các c:ng "r.nh Cịch #ụ c:ng cng% #à phá" "riển các s;n phqm mMi/ S?ng ph;i nhấn m'nh rng các ưMc "ính rủi ro ch] là m" "rong nhFng lo'i "h:ng "in được sO Cụng% #à các 4uy!" sách chấ" "h;i nguy h'i "hư+ng ị chi ph,i =i chính "rị% >t hi% inh "! hay các y!u ", hác)
Risk assessment pla%s a maMor role in the decision making for the remediation of contaminated sites 't provides an important part of the &asis for selecting from alternative remedies )see ection 1N*B+ Risks from e$posure are calculated for each alternative under the assumption that its remedial actions have &een implemented full% This ena&les a &alanced comparison of the effectiveness of each alternative at reducing risks (đánh giá rủi ro "r= "hành #ai "r 4uan "r-ng "rong #i*c >Dy Cựng các 4uy!" sách #$ #ấn đ$ "qy u! các địa điểm ị nhim đc/ f& cung cấp m" phen "h:ng "in n2n ";ng cho #i*c ch-n lựa các phương án "qy u! hác nhau (>Bm hen _|`)/ Sác rủi ro Co sự phơi nhim được "ính "oán cho mi phương án "rong sự gi; định rng các ho'" đng "qy u! của n& được "hực hi*n đey đủ/ Đi$u này giHp cho #i*c so sánh c:ng ng hi*u 4u; giFa các phương án để gi;m "hiểu các sự rủi ro)
Another application in site remediation is the esta&lishment of cleanup standards 'n man% cases, definitive numerical standards for specific contaminants in soil or groundwater simpl% do not e$ist Risk assessments are used to determine DHow clean is clean 'n this instance the calculation procedure is reversed The process starts with a numerical definition of accepta&le risk and works &ack to the level of contamination that will produce the accepta&le risk level An e$ample would &e a determination at a specific site that an% soil containing greater than @JJmgOkg of toluene would pose an unaccepta&le risk and thus has to &e remediated= soils containing smaller concentrations can &e left in place (m" 3ng Cụng hác "rong sự "qy u! địa điểm : nhim là "hi!" lJp các "i2u chuqn làm s'ch/ rong nhi$u "rư+ng hợp% các "i2u chuqn s, cu,i cRng cho mi chấ" đc h'i "rong đấ" hoác định 6['ch như "h! nào là s'ch7• rong nhFng hoàn c;nh này 4uá "rính "ính "oán này được nghịch đ;o/ vui "r.nh này " đeu #Mi m" định ngh5a s, h-c của sự rủi ro c& "hể chấp nhJn được #à nhFng #i*c 4uay "r= l'i m3c đ : nhim cái mà sZ s;n sinh ra m3c đ rủi ro c& "hể chấp nhJn được/ T" #í Cụ là m" sự >ác định "'i m" địa điểm cụ "hể rng ấ" Y lượng đấ" nào c& lượng "oluBnB lMn hơn Wxxmg~g sZ là rủi ro h:ng "hể chấp nhJn được #à #. #Jy cen ph;i được "qy u!U lo'i đấ" c& các n1ng đ nhA hơn c& "hể được đ<" #ào m" ch)
The EPA has proposed guidelines for the preparation of ha#ardous waste site risk assessments in a num&er of pu&lications The initial pu&lications, 0anCoo ^or SonCuc"ing nCangBrmBn" ssBssmBn"s and the [upBr^unC ulic 0Bal"h #alua"ion Tanual , have &een superseded &% is ssBssmBn" €uiCancB ^or [upBr^unC )RAQ+, the [upBr^unC >posurB ssBssmBn" Tanual , and the >posurB ac"ors 0anCoo RAQ, which comprises olumes ' and '', provides the site team risk assessor, remedial proMect manager )RPG+, and communit% involvement coordinator with information to improve communit% involvement in the uperfund risk assessment process olume ', Part A, provides suggestions for how uperfund staff and communit% mem&ers can work together during the earl% stages of uperfund cleanup 't identifies where, within the framework of the human health risk assessment methodolog%, communit% input can augment and improve the EPAFs estimates of e$posure
and risk= recommends .uestions the site team should ask the communit%= all illustrates wh% communit% involvement is valua&le during the human health risk assessment at uperfund sites olume ', Part ?, was prepared for risk assessors, remedial proMect managers and others to assist them in developing preliminar% remediation goals for !ational Priorities Sist )!PS+ sites pecificall%, RAQ, Part ?, provides guidance on using 9 Environmental Protection Agenc% to$icit% values and e$posure information to derive risk*&ased preliminar% remediation goals that are protective of human health olume ', Part C, offers guidance on the human health risk evaluations of remedial alternatives conducted during the feasi&ilit% stud%, during selection and documentation of a remed%, and during and after remed% implementation Part C assists users in preparing site*specific risk evaluations and maintaining fle$i&ilit% during the anal%sis and decision*making process olume ', Part , provides guidance on standardi#ed risk assessment planning, reporting, and review throughout the CERCSA remedial process, from scoping through remed% selection and completion and periodic review of the remedial action Part strives for effective and efficient implementation of uperfund risk assessment practice descri&ed in Part A, ?, and C, and in supplemental
14-/ )A0AR IENTI2IATI3N (fhJn C'ng nguy hiểm)
't is not uncommon to detect as man% as 1;; different chemicals at a contaminated site The ha#ard identification stage e$amines the data for all contaminants detected at a site and consolidates the data to stress the chemicals of concern )ie, those representing the vast maMorit% of risk posed &% the site+ Risk assessment re.uires a clear understanding of what chemicals are present at a site, their concentration and spatial distri&ution, and how the% could move in the environment from the site to potential receptor points The t%pes of data t%picall% sought at a ha#ardous waste site to address such needs are shown in Ta&le 14*:, and the collection of such data is detailed in Chapter 1@ A site investigation easil% can produce a huge amount of data, necessitating that steps &e taken in the ha#ard identification stage to facilitate su&se.uent anal%sis TA'+E 14-/ "t" nee!#
ite histor% (lịch sO hu đấ") Sand use (hi*n "r'ng sO Cụng đấ") Contaminant levels in media (m3c đ : nhim "rong các lMp "hành phen) Air, groundwater, surface water, soils and sediments (Lh:ng hí% nưMc ngem% đấ" #à lng c
Environmental characteristics affecting chemical fate and transport (các đ
Qeologic (địa chấ") H%dro*geologic ("hủy địa chấ"% địa chấ" "hủy #En) Atmospheric (hí 4uyển) Topographic (địa h.nh) Potentiall% affected population (hu CDn cư c& nguy cơ ị ;nh hư=ng) Potentiall% affected &iota (hu sinh #J" c& nguy cơ ị ;nh hư=ng)
The most to$ic, persistent, and mo&ile The most prevalent in terms of spatial distri&ution and concentration Those involved in the more significant e$posures The list of surrogate chemicals should encompass those chemicals that are estimated to account for KK percent of the risk at the site 't should contain compounds that will support an ade.uate evaluation of &oth carcinogenic and non*carcinogenic risk
Initi"$ Screenin( (sàng l-c an đeu)
ort the contaminant data &% medium )eg, groundwater, soil, etc+ for &oth carcinogens and non* carcinogens
/.
Ta&ulate for each detected chemical the mean and range of concentration values o&served at the site
.
'dentif% the reference concentrations for non*carcinogens and slope factors for carcinogens see Chapter @+ for each potential e$posure route
4.
etermine the to$icit% scores for each chemical in each medium >or non*carcinogens [ = S ma$ O ^S
(here
T
- to$icit% score
Cma$
- ma$imum concentration
)14*1+
RfC - chronic reference concentration )ie, an estimate of accepta&le dail% intake+ )see ection @*4, and /Bpa/go#~iris~ for the latest .ualitative and .uantitative data+ >or carcinogens [ = [ × S ma$
(here
>
- slope factor )also called carcinogen potenc% factor+
)14*:+
)see ection @*@, and and /Bpa/go#~iris~ for the latest .ualitative and .uantitative data+ 5.
>or each e$posure route, rank the compounds &% to$icit% scores
6.
>or each e$posure route, select those chemicals comprising KK percent of the total score The process is illustrated &% the following two e$amples ata for surface soils appear in Ta&le 14*I Reference concentrations and slope factors ma% &e found in the EPAFs 'R' data&ase, or in other sources of to$icological information E5AM%+E 14-1. SE+ETI3N 3N N3NARIN36ENI )EMIA+S Rank the chemicals for
soil in Ta&le 14*I
emic"$
m"7, m(8(
3r"$ Rf9
To7icity #core
R"n
Chloro&en#ene
B4;
:;; $ 1;*:
I:; $ 1;:
I
Chloroform
41;
1;; $ 1;*:
41; $ 1;:
:
1,:*ichloroethane
!
!A
!A
!A
?EHP !A not applica&le [ourcB 'R'
:I; $ 1;
:
:;; $ 1;
11@ $ 1;
*:
1
4
E5AM%+E 14-/. SE+ETI3N 32 ARIN36ENI )EMIA+S Rank the chemicals for soil in
Ta&le 14*I emic"$
m"7, m(8(
3r"$ S29
To7icity #core
R"n
Chloro&en#ene
B4;
!A
!A
!A
Chloroform
41;
B1; $ 1;*I
:@; $ 1;*:
:
1,:*ichloroethane
!
K1 $ 1;:
!A
!A
I::
1
:
?EHP !A not applica&le [ourcB 'R'
:I; $ 1;
*:
14; $ 1;
!ote in E$amples 14*1 and 14*: that ?EHP )is*:*eth%l he$%l phthalate+ and chloroform have &oth carcinogenic and non*carcinogenic to$icit% so that the% appear in &oth rankings TA'+E 14- emic"$ concentr"tion# "t A' $"n!fi$$ Air
emic"$
Chloro&en#ene Chloroform 1,:*ichloroethane ?EHP ! not detected
6roun! w"ter
Soi$
Me"n, m(8m
M"7imum, m(8m
Me"n, m(8+
M"7imum, m(8+
Me"n, m(8(
M"7imum, m(8(
4;K $ 1;*J 11; $ 1;*1: 14; $ 1;*J I:K $ 1;*N
J;K $ 1;*J I1: $ 1;*1: :4; $ 1;*J J:K $ 1;*N
:@; $ 1;*4 4I; $ 1;*4 :1; $ 1;*4 !
11; $ 1;*: NB; $ 1;*I :;; $ 1;*I !
1IK 11: ! 1;I $ 1;:
B4; 41; ! :I; $ 1;:
2urter Screenin( of emic"$#
The ranking of to$icit% scores as illustrated &% the previous e$amples indicate which compounds pose the greatest ha#ard &ased solel% on their ma$imum concentration and to$icit% The selection of chemicals of concern re.uires further evaluation to consider for each chemical its range of concentrations, its mo&ilit% in the environment, and other issues These additional considerations include •
Gean concentration (n1ng đ "rung .nh)
•
>re.uenc% of detection ("en suấ" phá" hi*n)
•
Go&ilit% ("ính C i!n đ@i)
•
Persistence in the environment (sự "1n lưu lDu Cài "rong m:i "rư+ng)
•
Chemicals associated with site operation (các chấ" h&a h-c )
•
Treata&ilit% 'n general, chemicals with a low fre.uenc% of detection or e$tremel% low mean concentration are not deemed sufficientl% significant to receive direct evaluation The evaluation of mo&ilit% in the environment uses information such as half*lives and ph%sical*chemical properties )Henr%Fs law constant, vapor pressure, octanol*water partition coefficient and solu&ilit%+ )see ection I*:+ Chemicals whose persistence and mo&ilit% make them significant risks would remain in the list of chemicals of concern Also, the risk anal%st can selectivel% add compounds that are degradation products of others on the list )eg, vin%l chloride from TCE+ Although, the list of chemicals of concern should account for a&out KK percent of the risk, it ma% account for less than 1; percent of the detected chemicals 't is not infre.uent to reduce a total of 1;; detected chemicals to 1; to 1@ chemicals of concern
14- E5%3SURE ASSESSMENT (Đánh giá phơi nhim)
The second stage of a .uantitative risk assessment consists of estimating the e$posure to the chemicals &% the populations potentiall% at risk To provide a comprehensive understanding of the sources of contamination, this stage &egins with a delineation of the sources )eg, sludge lagoons, contaminated soil+ and the spatial distri&ution of contaminants at the site The e$posure assessment continues &% anal%#ing how the contaminants might &e released Qiven the release of a chemical, it is necessar% to estimate how it ma% migrate )eg, via groundwater+ to a potential receptor )eg, users of groundwater+ Having identified current and potential receptor points, considera&le attention is given to )1+ identification of general and sensitive populations of current and potential receptors and ):+ estimation of &oth short* and long*term e$posures in terms of doses &% e$posure route Environment"$ %"tw"y#
Guch of this stage consists of a fate and transport anal%sis as presented in depth in Chapter 4, and onl% a &rief summar% will &e presented here A chain of events must occur to result in e$posure This chain in a collective sense is termed an environmental pathwa% )ie, the environment routes &% which chemicals from the site can reach receptors+ A pathwa%, consisting of the following elements, thus defines the framework of a fate and transport anal%sis • • • • • • • •
ource )eg, a lagoon+ Chemical release mechanism )eg, leaching+ Transport mechanisms )eg, groundwater flow+ Transfer mechanisms )eg, sorption+ Transformation mechanisms )eg, &iodegradation+ E$posure point )eg, residential well+ Receptors )eg, residential consumers of drinking water+ E$posure route )eg, ingestion+ An e$ample of two simple &ut common pathwa%s, one involving groundwater and the other atmospheric transport, is shown in >igure 14*1
transport 't is necessar% to esta&lish potential pathwa%s &etween sources and receptors for each chemical of concern >igure 14*: is a flowchart indicating the t%pes of considerations necessar% in anal%#ing fate and transport at ha#ardous waste sites ont"min"nt Re$e"#e, Tr"n#ort, Tr"n#fer, "n! Tr"n#form"tion
The release of contaminants from ha#ardous waste sites results from natural processes, such as leaching of solu&le chemicals to groundwater= human activit%, such as the construction of site drainage channels= and accidents such as chemical spills Ta&le 14*4 summari#es some potential mechanisms for release of chemicals 2I6URE 14-1 E$amples of
e$posure pathwa%s
2I6URE 14-/A >lowchart for fate and transport assessments of the atmosphere
'n addition to determining what chemicals are released from a source, it is important to determine what happens to these chemicals how the% are transported, transferred, or transformed Transport involves movement &% advection and diffusion A great num&er of mechanisms could act to transfer the contaminants to another medium or to storage sites )eg, sorption onto soils+ 'n some instances, organic contaminants transform under environmental mechanisms to C<: and water, while in others cases the degradation products ma% &e more to$ic than the original chemical )eg, reductive dechlorination of tetrachloro* and trichloroeth%lene to vin%l chloride+ E$ample mechanisms for the transfer and transformation of chemicals are presented in Chapter 4, and several e$amples are shown in Ta&le 14*@ %otenti"$$y E7o#e! %ou$"tion#
The ne$t step in the e$posure assessment is to determine potentiall% e$posed populations These would include the following •
Present population in vicinit% of the site
•
>uture population in vicinit% of the site
•
u&populations of special concern )eg, %oung children in the case of lead contamination+
•
Potential on*site workers during an% remediation The present population ma% &e initiall% identified as those living within specified distances from site &oundaries )eg, 1 and I miles+ However, an% distance could &e specified, depending on the results of the fate and transport anal%sis etermining potentiall% e$posed populations is &ased on the surrounding land use and documented sources of demographic information such as summari#ed in Ta&le 14*B 2I6URE 14-/' >lowchart for fate and transport assessment in surface water
2I6URE 14-/ >lowchart for fate and transport assessment in
and sediment
surface water and sediment
TA'+E 14-4 ont"min"nt Re"$e"#e mec"ni#m# Me!i"
Mec"ni#m
Time 2r"me
Air
olatili#ation >ugitive dust generation Com&ustion Erosion Seachate generation pills Seachate generation pills
C C, E E C, E C E C E
oil
urface and groundwater C Chronic
E * Episodic
TA'+E 14-: Mec"ni#m# "ffectin( environment"$ tr"n#fer "n! tr"n#form"tion of cemic"$#9 2"te mec"ni#m Me!i"
Tr"n#fer
Tr"n#form"tion
(ater
olatili#ation Adsorption 9ptake &% plants issolution in rainwater (ashout &% rain Qravitational deposition
?iodegradation Photochemical degradation ?iodegradation
oil Atmosphere
<$idation &% o#one
Adapted from RA Conwa% 14
After a preliminar% overview of documents has &een made, a thorough site visit to Dground truth the current situation is critical Patterns of human activit% associate with various land and water uses should &e determined, including answering .uestions such as •
(hat sort of sensitive pu&lic facilities are located near the site )eg, schools, hospitals, da% care centers, nursing homes+ TA'+E 14-; Source# of !emo(r"ic inform"tion
Topographic maps (;n đ1 địa h.nh) Census reports (áo cáo đi$u "ra CDn s,)
Ta$ maps (;n đ1 "hu! #ụ) Count%Oregional demographic studies
Gunicipal #oning maps (;n đ1 #Rng đ: "hị) ProMected future land use
(các nghi2n c3u nhDn hqu h-c "hBo đơn #ị hành chính~ "hBo #Rng) Sand use data (s, li*u đấ" sO Cụng) ite visit ("hEm hi*n "rư+ng) Human activit% patterns (các m: h.nh sinh ho'" của con ngư+i)
(Ci*n "ích đấ" Cự i!n sO Cụng "rong "ương lai) Aerial photos (;nh chụp "d "r2n h:ng)
•
•
•
(hat outdoor activities occur )eg, parks, pla%grounds, recreational facilities near&%+ (hat fraction of time do various su&populations spend in potentiall% contaminated area )eg, children in a grade school+ (hat is likel% to change )eg, seasonall%, immediate future, long*term future+
•
•
(hat secondar% e$posures are possi&le )eg, contamination of crops at near&% farms+ (hat are the dietar% ha&its )eg, consumption of recreational fish containing &io* accumulated contaminants+ Certain su&populations ma% re.uire special consideration &ecause of their higher sensitivit% to to$ic su&stances * children, pregnant women, the elderl%, and people with chronic illnesses An initial step in identif%ing such su&populations is to locate sensitive facilities such as schools and nursing homes 't is critical to evaluate future populations to address how changes could affect the estimates of risks >or e$ample, if groundwater is not currentl% utili#ed as a drinking water source &ut could &e used in the future, this ma% dramaticall% affect future risk calculations
eve$oment of E7o#ure Scen"rio#
After potential populations and e$posure pathwa%s have &een defined, it is then necessar% to characteri#e the conditions under which the populations ma% &e potentiall% e$posed This involes an evaluation of &oth current and reasona&le future uses of the site to esta&lish a credi&le set of conditions under which the e$posure could occur After the scenarios have &een esta&lished, then the specific parameters governing e$posure )eg, e$posure fre.uenc%, duration, and intake rate+ can &e selected ome e$amples of commonl% used e$posure scenarios include a worker scenario, a trespasser scenario, a residential use scenario, a recreational use scenario, and a construction scenario Each of these is discussed in the following listing, together with some pertinent .uestions for the risk assessor to consider in determining whether site conditions warrant evaluation of the given scenario •
the site currentl% used for industrial activities Are workers e$posed to site* related constituents under normal conditions Could workers &e e$posed in the future, either &ecause of a change in use of the site or &ecause the workers would &e involved in remedial activities 't should &e note that workers are strictl% protected under
•
Tre#"##er #cen"rio= 's
there evidence that trespassing ma% routinel% occur at the site 's there a fence that would limit access to the site 'f so, is the fence in good condition Have other measures &een taken to limit access to the site 's the site close to a school, shopping, or residential area where area children would have reason or inclination to pla% at the site 's the site attractive to children 's the site currentl% used for residential purposes (ill it or could it &e used for residential purposes in the future Are there an% #oning or deed restrictions that would limit its use for residential purposes Are the residences singe*famil% dwelling 's there the potential for residential use of groundwater A residential scenario is fre.uentl% evaluated as a h%pothetical condition in an effort to estimate worst*case risks E$posure under a residential scenario is generall% the most restrictive condition for an% age group, thus resulting in the greatest potential e$posures and the highest potential risks
•
Re#i!enti"$ u#e #cen"rio=
•
Recre"tion"$ u#e #cen"rio=
This scenario is particularl% applica&le for evaluation of potential risks associated with sureface water &odies where people ma% fish, swim, canoe, wade, etc <&servations made during site investigation activities can &e useful in the development of a recreational e$posure scenario 't ma% also &e important to confirm the regulated use and classification of the water &od% with the appropriate state of federal agenc%
•
on#truction #cen"rio= Are
construction activities planned or likel% at the site (ill the construction result in potential e$posures for &oth on*site receptors )eg, direct contact with soils &% construction workers+ and off*site populations )eg, e$posure &% off*site residents or workers to fugitive dust and volatiles released as a result of earth*moving activities+
The development of scenarios involves making assumptions and must include su&Mective decisions 'deall%, this should produce credi&le scenarios, &ut in an effort to ensure conservative risk assessments, unrealistic scenarios have &een used at some ha#ardous waste sites As an e$ample, pica &ehavior is a real phenomenon and should &e considered, &ut the assumption that children will eat :;;mgOda% of soil for a N;*%ear lifetime is not realistic !ondegradation policies, in man% states, prohi&it the discharge of contaminants into streams, independent of the present water .ualit% in the stream That polic% has &een used to suggest that a stream heavil% contaminated with acid mine drainage &e considered a primar% drinking water source for the purpose of developing a credi&le scenario for a risk management The point is that while nondegradation ma% &e an appropriate pu&lic polic%, drinking acid mine drainage is not realistic E7o#ure oint# define the locations of the receptors for the various scenarios The% are identified for
each e$posure scenario simpl% &% overla%ing the demographic information with the e$posure pathwa% An e$posure point ma% &e as close as the sources of waste at the site itself )eg, the trespasser scenario+ or at considera&le distance, particularl% for pathwa%s involving the food chain E7o#ure %oint oncentr"tion#
The risk anal%st must ne$t estimate the concentration of contaminants at the e$posure points, including all pathwa%s air, ground and surface water, soils, sediments, and food )eg, plants and fish+ >or present e$posures, actual monitoring data at the e$posure point should &e used wherever possi&le >or e$ample, contaminant concentrations should &e o&tained for drinking water wells in the vicinit% of a site >or on*site e$posure points, representative concentrations in soil or groundwater ma% &e calculated as the arithmetic or geometric mean )depending on the statistical distri&ution of the site anal%tical concentration data+ >uture conditions can differ starkl% A plume ma% not have %et migrated to a potential e$posure point Remediation will, of course, drasticall% reduce migration 'n a comprehensive risk assessment, the e$posure concentrations for each remedial alternative would &e estimated including the present situation )&aseline conditions or no remedial action+ etermining the concentration of a contaminant at the e$posure point for future conditions often re.uires the use of fate and transport modeling methods of Chapter 4 and standard references The maMor effort with these models is cali&ration= once cali&rated, successive runs can &e made relativel% easil% to estimate concentrations for a range of conditions and assumptions >or groundwater contaminants, h%drogeologic models can &e used to estimate the future concentration at a downstream well >or volatile organic compounds released to the atmosphere, a gaussian diffusion model can &e emplo%ed to estimate future downwind concentrations 'n general, the level of effort emplo%ed in data collection and modeling will depend on the estimated severit% of the risk !ominal risks do not warrant the same level of anal%sis as the clearl% significant risks All mathematical models re.uire the making of assumptions 't is essential that the appropriateness of assumptions &e reviewed carefull% The impact of assumptions on the e$posure point concentrations and, ultimatel%, the risk values should &e e$amined through a sensitive anal%sis A sensitive anal%sis identifies which of the m%riad of input varia&les have the most significant impact on the resulting risk value Recetor# o#e#
The final step in the e$posure assessment stage is to estimate the doses of the different chemicals of concern to which receptors are potentiall% e$posed at the e$posure points As with the previous stages, three e$posure routes are considered*insgetion, inhalation, and dermal contact Also, there are three t%pes of doses the
administered dose )the amount ingested, inhaled, or in contact with the skin+, the intake dose )the amount a&sor&ed &% the &od%+, and the target dose )the amount reaching the target organ+ >or purposes of calculating risks, the dose should &e in the same form as that of the dose*response relationship reported for the specific chemical and the e$posure route under stud% This will almost alwa%s &e either administered dose or a&sor&ed dose Qiven the concentration of the contaminant at the e$posure point, the calculation of administered dose is straightforward 'n contrast, the calculation of a&sor&ed dose &ased on administered dose re.uires consideration of some comple$ factors )see ection @*1+ The ke% factors influencing the uptake of contaminants &% the &od% are simplified as follows 'ngestion
'nhalation
ermal contact
Contaminant concentration in the ingested media Amount of ingested material ?ioavaila&ilit% to the gastrointestinal s%stem Concentration in air and dust Particle si#e distri&ution ?ioavalla&ilit% to the pulmonar% s%stem Rate of respiration Concentration in soil and dust Rate of deposition of dust from air irect contact with soil ?ioavaila&ilit% Amount of skin e$posed
(here
' C CR E> E ? AT
S × S × × z V‚ × p
)14*I+
- intake )mgOkg of &od% weight da%+ - concentration at e$posure point )eg, mgOS in water or mgOmI in air+ - contact rate )eg, SOda% or mIOda%+ - e$posure fre.uenc% )da%sO%ear+ - e$posure duration )%ears+ - &od% weight )kg+ - averaging time )da%s+
E.uation 14*I is t%picall% modified for specific e$posure pathwa%s >or e$ample, the intake dose from inhalation of fugitive dust ma% &e calculated as { =
(here
S × S × × z × × ps V‚ × p
RR
- retention rate )decimal fraction+
A&s
- a&sor&tion into &loodstream )decimal fraction+
)14*4+
>or fugitive dust, the concentration in the air is determined &% S = S s
× c
)14*@+
(here
Cs
- concentration of chemical in fugitive dust )mgOmg+
Pc
- concentration of fugitive dust in air )mgOmI+
or e$ample,in the evaluation of a trespasser scenario, o&servations of trespassers during site investigation activities ma% dictate the values used for e$posure fre.uenc% )eg, num&er of da%s per %ear or num&er of events per %ear+ and e$posure duration )eg, num&er of %ears that the activit% occurred+ Common sense also pla%s an important role in the selection of e$posure parameters >or e$ample, if one were evaluating residential use of two sites, one in !orth akota and one in >lorida, it would not &e reasona&le to assume the e$posure fre.uenc% )eg, da%s per %ear that an activit% ocurred+ would &e the same in the two risk assessments for a child potentiall% e$posed to surface soils as a result of their pla%ing outdoors in the &ack%ard Averaging time )AT+ is another important parameter that must &e defined in the intake e.uation The averaging time selected will depend on the t%pe of constituent &eing evaluated >or e$ample, to assess long* term or chronic effects associated with e$posure to noncarcinogens, the intake is averaged over the e$posure duration )e$pressed in da%s+ )The averaging time is e.ual to the e$posure duration for noncarinogens+ E$posure to carcinogens, however, is averaged cover a lifetime )assumed to &e N; %ears or :@,@@; da%s+, to &e consistent with the approach used to develop slope factors TA'+E 14-> St"n!"r! "r"meter# for c"$cu$"tion of !o#"(e "n! int"e !etermine! for te A' $"n!fi$$ %"r"meter
A!u$t#
i$! "(e ;-1/
i$! "(e /-;
Average &od% weight )kg+ kin surface area )cm:+ (ater ingested )SOda%+ Air &reathed )mIOh+ Retention rate )inhaled air+ A&sorption rate )inhaled air+ oil ingested )mgOda%+ ?athing duration )minutes+ E$posure fre.uenc% )da%sO%ear+ E$posure duration )%ears+
N; 1J,1@; : ;JI 1;;L 1;;L 1;; I; IB@ I;
:K 1;,4N; : ;4B 1;;L 1;;L 1;; I; IB@ B
1B B,KJ; 1 ;:@ 1;;L 1;;L :;; I; IB@ 4
An e$ample of the parameters used for this t%pe of calculation are shown in Ta&le 14*N 't should &e noted that these values can var% greatl%, depending on the assumed e$posure conditions )ie, the selected e$posure scenario+ As an e$ample, the air &reathing rate for adult males is ;JImIOh in Ta&le 14*N However, this rate can var% &% an order of magnitude from ;Bm IOh at rest to N1mIOh for vigorous ph%sical e$ercise 't should &e noted that carinogenic and noncarcinogenic human health risks are often computed &% using &oth average and ma$imal chemical intakes The purpose of using &oth values is to calculate most pro&a&le and worst*case risks, two end points that ma% have meaning to either regulators or potential receptor populations E5AM%+E 14-A. A+U+ATI3N 32 3NTAMINANT INTAKE. etermine the chronic dail% inhalation
intake, &% adults in a residential setting, of a noncarcinogenic chemical as a function of concentration in fugitive dust at the A?C Sandfill )Ta&le 14*I+
Solution. >or an adult e$posed to a noncarcinogenic constituent, the intake { f ma% &e calculated from E.uation 14*I { f
( S × S × × z × × ps)
=
V‚ × p
>rom Ta&le 14*N, air &reathing rate for adults - ;JI m IOh CR E>
- ;JI mIOh $ :4 hOda% - 1KK: m IOda% - IB@ da%sO%ear
>or residential e$posures, a default value of E - I; %ears is t%picall% used 'n the a&sence of &etter information, a conservative approach would assume the retention rate )RR+ and the a&sorption into &loodstream would &oth e.ual 1;; percent or 1; ?( - N;kg )Ta&le 14*N+ AT - IB@ da%sO%ear $ I; %ears - 1;,K@; da%s { f
S × 1K K: × IB@ × I; × 1; × 1; N; × 1;,K@;
=
I - ;:J@ m O)kg da%+ $ C
(here C - e$posure point concentration )mgOm I+ E5AM%+E 14-'. A+U+ATI3N 32 3NTAMINANT INTAKE.
etermine the chronic dail% inhalation intake
in children age B*1: of a carcinogenic chemical )ie, calculate { S+ Solution. { S
=
S × S × × z × × ps V‚ × p
>rom Ta&le 14*N CR E> E RR ?(
- ;4B mIOh $ :4 hOda% - 11;4 m IOda% - IB@ da%sO%ear - B %ears - A&s - 1; as in E$ample 14*Ia - :K kg )Ta&le 14*N+
The averaging time )AT+ for determining carcinogenic risk is N; %ears or :@,@@; da%s As noted in the te$t, this is to &e consistent with the approach used to develop carcinogenic slope factors { S
=
S × 11 ;4 × IB@ × B × 1; × 1; :K × :@,@@;
I - I:B $ 1; *: m O)kg da%+ $ C
(here C - e$posure point concentration )mgOm I+ etermine the average dail% intake of chloro&en#ene over 1 %ear of e$posure for on*site workers from dermal contact of the soil in Ta&le 14*I E5AM%+E 14-4A. AVERA6E AI+? INTAKE 2R3M ERMA+ 3NTAT
Assume the following additional parameters A - skin e$posed - :;L - ;: $ 1J,1@; cm : - IBI; cm : A - dust adherence - ;@1 mgOcm : A&s - skin a&sorption rate - BL G - effect of soil matri$ - 1@L )ie, &ecause of soil matri$, onl% 1@L of contamination is actuall% availa&le for contact+
E> E ?( AT
- two e$posure events per da%= 1@B e$posure da%s per %ear - 1 %ear - N; kg - IB@ da%s or 1 %ear
Solution.
mg zp mg × ps × [T × : e$p B#Bn"s × 1@BCays × z × )gsoil × p( cm : ) × )g Cay yBar e$p B#Bn" cm : 1; B mgsoil = S
{ f
-
S × IBI; × ;@1 × ;;B × ;1@ × : × 1@B × 1× 1; −B N; × IB@
- ):;I $ 1;*N $ C+ mgO)kg da%+ >rom Ta&le 14*I, the average concentration of chloro&en#ene in soil is 1IK mgOkg The dail% intake of chloro&en#ene is 1IK mgOkg $ :;I $ 1; *N { f - :J: $ 1; *N mgO)kg da%+
Thus,
etermine the average dail% intake of chloroform for on*site workersfrom dermal contact os the soils in Ta&le 14*I Assume that the intake estimate will &e used to assess the carcinogenic effects of chloroform )oe, calculate { S+ E5AM%+E 14-4'. AVERA6E AI+? INTAKE 2R3M ERMA+ 3NTAT
Solution. S × p × { S
=
zp e$p B#Bn"
×
ps × [T ×
: e$p B#Bn"s
Cay
×
1@BCays
yBar
×
z ×
)g 1; B mg
V‚ × p
S × IBI; × ;@1 × ;;B × ;1@ × : × 1@B × 1; −B N; × :@,@@;
- :K1 $ 1;*K $ C >rom Ta&le 14*I, the dail% intake of chloroform is 11: mgOkg $ :K1 $ 1; *K Thus, { S - I:B $ 1; *K mgO)kg da%+ 't should &e noted that unlike the oral and inhalation routes, there are no generall% accepted reference concentrations or slope factors for the dermal route 'n lieu of these, oral RfCs and > values ma% &e utili#ed, &ut the advice of a .ualified to$icologist should &e sought
E.uation similar to those developed in E$amples 14*I and 14*4 are used in spreadsheets to calculate administeredOa&sor&ed doses for all chemicals of concern for all pathwa%s These are repeated for each e$posure scenario 14-4 T35IIT? ASSESSMENT
This stage of the risk assessment process defines the to$icit% )ie, the dose*response relationship+ for each chemical of concern The output takes the form of mathematical constants for insertion into risk calculation e.uations 'n addition to providing a set of mathematical constants for calculating risk, the to$icological
assessment should also anal%#e the uncertaint% inherent in these num&ers, and descri&e how this uncertaint% ma% affect the estimates of risk Chapter @ e$plains in detail the scientific &asic underl%ing the development and application of dose* response relationships This section highlights some of the important concepts and .uantitative methods involved in such undertakings and how the% appl% to the calculation of the risk from e$posure to ha#ardous waste constituents "rcino(en# ver#u# Nonc"rcino(en#
>or the purposes of .uantif%ing human health risks, chemicals are characteri#ed as carcinogens )ie, those with demonstrated propensit% for cancer induction+ and noncarcinogens ome chemicals &ehave as &oth carcinogens and noncarcinogens and, hence, will appear in &oth t%pes of calculation of potential human health risk Carcinogens tend to dominate pu&lic concerns a&out health risk= however, this is not the reason for distinguishing &etween chemicals that induce cancer and those that do not The distinction is important &ecause the two elicit to$ic responses in different wa%s, giving rise to two .uantitativel% different models for induction of to$ic response as a function of dose Thus, the mathematical e$pressions of risk differ for the two categories of chemicals !oncarcinogens have thredholds &elow which the% fail to induce an% discerni&le adverse health effect 'n contrast, a linear nonthreshold model has &een adopted for all carcinogens &% the EPA )see >igure @*:4+ According to this model, some risk is assumed for carcinogens at an% dose, regardless of how small There is increasing evidence, however, that some carcinogens do have thresholds, especiall% those that function as promoters Source# of To7icity "t"
The e$perimental research effort involved in developing a new dose*response relationship for a to$ic su&stance takes considera&le time, much longer than associated with starting and completing a stud% of most ha#ardous waste issues Rather than conduct e$perimental research, the risk anal%st defers to e$isting data found in standard sources of to$icological data, and selects from them the appropriate mathematical descriptors of to$icit% Perhaps the most used source is 'R' )'ntergrated Risk 'nformation %stem+ The to$icologic indices in the 'R' data&ase are updated continuousl% and availa&le on*line )wwwepagovOirisO+ The 'R' data&ase contains &oth .ualitative and .uantitative data regarding noncarcinogens as well as carcinogens 't should &e noted that regulator% agencies will fre.uentl% specif% the particular mathematical constants to &e used (hether taken from regulator% guidance or other sources, the to$icit% constants must appl% to the range of doses predicted &% the e$posure assessment Also, &ecause to$ic response for the same dose can var%, depending on the e$posure route, a separate to$icit% constant fre.uentl% must &e selected for each e$posure route predicted &% the e$posure assessment S$oe 2"ctor# for "rcino(en#
Reference oncentr"tion# for Nonc"rcino(en# %rotective N"ture of E%A Aro"c 14-: RISK )ARATERI0ATI3N Ri# for Aver"(e "n! M"7imum E7o#ure# "rcino(enic Ri#
Nonc"rcino(enic Ri# '"c(roun! Ri# Iter"tive N"ture of Ri# A##e##ment Uncert"inty Inerent in "$cu$"te! Ri##
14-; RISK 3MMUNIATI3N
Having characteri#ed the risk of e$posure to consituents of ha#ardous waste and the degree of uncertaint% associated with the risks, the ne$t step is to use the information to improve the &asis for making decisions This often involves the pu&lic, or at least em&races pu&lic concerns and attitudes 't re.uires an e$amination of the .uestion, D(hat is accepta&le risk 't enters the area of perception, and while not leaving the world of science, it is much different world and one not relished &% man% scientists and engineers ([au hi >ác định được các đ
<"t i# Accet"&$e Ri#@
At present the EPA has defined accepta&le risks for carcinogens as within the range of 1; *4 to 1;*B e$cess lifetime cancer risk and for noncarcinogens as a ha#ard inde$ of less than 1; As discussed in ection @*@, there have &een precedents with other issues which have defined Daccepta&le risk outside this range The 9 >A deemed that less than 1; *N cancer risk for saccharin was Daccepta&le, and local citi#ens were willing to accept a risk much greater than 1; *4 for a copper smelter Clearl%, Daccepta&ilit% is a personal concept and demands that the pu&lic, which ultimatel% must have Murisdiction over what level of risk is accepta&le, &e informed At man% sites it is ultimatel% the pu&lic that determines &% its influence which levels of potential health risks are accepta&le The EPA uses 1; *B e$cess lifetime cancer risk as a point of departure, meaning that higher risk ma% &e deemed acepta&le onl% if there was special e$tenuating circumstances >or purposes of comparison, e$amples of actions that would increase the risk of death &% a pro&a&ilit% of 1 $ 1; *B are illustrated in Ta&le 14*1; Almost all of the actions shown in Ta&le 14*1; seem highl% accepta&le if not commonplace= %et, the magnitude of their risk compares with that of the EPAFs target risk for ha#ardous waste sites 't should &e noted that risk of cancer is not the same as risk of death &ecause not all cancer cases result in death till, cancer is the second greatest cause of death in the 9nited tates TA'+E 14-1 Action# incre"#in( ri# of !e"t &y one in " mi$$ion Action
N"ture of ri#
moking 14 cigarettes rinking ;@ liter of wine pending 1 hour in a coal mine pending I hour in a coal mine Siving : da%s in !ew Uork or ?oston Traveling B minutes &% canoe Traveling 1; miles &% &ic%cle Traveling I; miles &% car >l%ing 1;;; miles &% Met
Cancer, heart disease Cirrhosis of the liver ?lack lung disease Accident Air pollutionO heart disease Accident Accident Accident Accident Cancer caused &% radiation Cancer, heart disease Siver cancer caused &% Aflatto$in ?1
rinking heavil% chlorinated water )eg, Giami+ for 1 %ear rinking thirt% 1:*o# cans of diet soda Siving @ %ears at site &oundar% of a t%pical nuclear power plant in the open Siving 1@; %ears within :; miles of a nuclear power plant Eating 1;; charcoal*&roiled steaks
Cancer caused &% chloroform Cancer caused &% saccharin Cancer caused &% radiation Cancer caused &% chloroform Cancer from &en#o)a+p%rene
Another comparison is that of incremental risk and &ackground risk The 1; *B target represents an incremental risk of ;;;;1 perent pro&a&ilit%, an especiall% small level in comparison to the :@ percent &ackground risk of the ver% same disease for which this regulator% target is directed The total risk to an individual e$posed at the EPAFs target would increase from :@ percent to :@;;;1 percent This increase is hardl% meaningful from a scientific perspective, especiall% considering that the e$posed population is not the whole nation &ut isolated pockets Ri# %ercetion
(hile an increase in cancer risk &% an increment of 1; *B ma% not &e significant from a scientific viewpoint, it easil% can alarm the communit% near a ha#ardous waste siteThe reason is perception ome of the factors that affect the perception of risk are indicated in Ta&le 14*11 and are discussed in ection 1*4 The factors work in such a manner that, for e$ample, an action #olun"arily undertaken &% an individual is perceived as posing a smaller risk than one imposBC on that individual, all else &eing e.ual Almost all of the Dmore risk% items are associated with ha#ardous waste Clearl%, the four*stage risk assessment process descri&ed on the preceding pages can not incorporate such factors in a precise .uantiative calculation TA'+E 14-11 Ri# ercetion +e## ri#y
More ri#y
oluntar% >amiliar Controlled &% self Chronic !atural >air etecta&le !ot memora&le
'nvoluntar% 9nfamiliar Controlled &% others Acute Artificial 9nfair 9ndetecta&le Gemora&le
A concept accompan%ing pu&lic perception is the notion of accepta&le risk >ischoff, et al identified five generic comple$ities that affect accepta&le risk •
•
•
•
•
efining the decision pro&lem Assessing the facts Assessing relative values Addressing the human element in decision*making processes Assessing the .ualit% of the decisions
(ith each of these, there is a perception gap &etween the decision makers and the local citi#ens tarting with the first item, a decision makerFs resposi&ilit% in site remediation clima$es with the evaluation of several remedial alternatives and the selection of one The pu&lic likel% will view this evaluation as an unnecessar% e$ercise The% will ask, D(h% deli&erate when it has &een intuitivel% clear from the onset that the safest decision is to e$cavate the waste and haul it out of their communit% The difficulties that surround assessing the facts are primaril% those of dealing with the large magnitude of uncertaint% inherent in an% risk assessment
purposeful use of conservative safet% factors at each stage to protect human health serves to inflate resulting risk num&ers, and the pu&lic will often e$press more concern with the possi&le magnitude of the worst*case scenario, either not understanding or electing to ignore how unlikel% if not incredi&le it ma% &e Gerel% learning that the assessment is filled with uncertaint% ma% make the pu&lic uneas% a&out the estimates, &elieving that the true risk ma% &e even greater than indicated 't is important to note that almost all of the resources applied in risk assessment are devoted to the first two items of >ischoffFs list The local citi#ensare Must as influenced, perhaps more so, &% the other three Concentrating resources on the first two items is thought &% decision makers to portra% their decisions as purel% o&Mective inall%, rarel% do decision makers revisit the issue long after the decisions have &een made to determine if the decision was a good one and whether their decision*making process needs adMustment (ere the right .uestions asked id we solve the real pro&lems Ri# ommunic"tion
't is perhaps now understanda&le that, given the five comple$ities listed &% >ischoff, DThe pu&lic often sees proponents of risk assessment as tr%ing to convince people to accept risks that the proponentsdo not face rather than acting to remove them !ot suprisingl%, the remed% desired &% the pu&lic is to remove the ha#ardous waste to Dsomewhere else even though in scientific terms this ma% pose the largest risk (hile it is possi&le to provide reasona&le .uantiative estimates of risks, it is clear from the previous discussion that it is ver% difficult to e$plain these risks to the affected pu&lic This derives onl% in part from the highl% technical nature of the risks assessment process At man% site, the selection of an alternative is driven &% the demands of the citi#ens living in the vicinit% of the site 't is therefore essential that consideration &e given to communicating risks as well as calculating them antos and Edwards suggest that to achieve effective risk communication three .uestions must &e answered •
•
•
's the communicator listening and acknowledging the concerns of the audience How capa&le is the spokesperson Can the o&Mectives of the presentation &e met while still meeting the information needs of the pu&lic
14-> E3+36IA+ RISK ASSESSMENT9 "r"teri*"tion of '"#e$ine Eco$o(y Eco$o(ic"$ To7icity A##e##ment Eco$o(ic"$ E7o#ure A##e##ment Eco$o(ic"$ Ri# "r"cteri*"tion 14-B M3NTE AR+3 MET)3S Stoc"#tic ver#u# etermini#tic "$cu$"tion# Meto! e#crition
An E7"m$e 14-C ASE STU? )"*"r! I!entific"tion E7o#ure A##e##ment To7icity A##e##ment Ri# "r"cteri*"tion ISUSSI3N T3%IS AN %R3'+EMS
