Bioremediation: Week 2
• Setting goals for groundwater
cleanup (Regulations)
• Risk Assessment
Cleanup goals under CERCLA
• National Contingency Plan (for the Superfund)
Ground water cleanup goals should meet chemical-specific
“applicable or relevant and appropriate requirements” from other
regulations, known as ARARs.
Drinking water standards: (1) The Safe Drinking Water Act
(Maximum Contaminant Levels [MCLs]); (2) State drinking water
standards.
Direct discharges to surface water: must meet federal requirements
(the Clean Water Act)
Cleanup goals under CERCLA
• National Contingency Plan (for the Superfund)
Ground water cleanup goals should meet chemical-specific
“applicable or relevant and appropriate requirements” from other
regulations, known as ARARs.
Drinking water standards: (1) The Safe Drinking Water Act
(Maximum Contaminant Levels [MCLs]); (2) State drinking water
standards.
Direct discharges to surface water: must meet federal requirements
(the Clean Water Act)
•If no ARAR exists for a particular chemical, the ground water
clean-up goal is based on risk assessment.
In general, cleanup goals based on risk assessments must result in
a risk level of 10-4 to 10-6 for carcinogens and a hazard index of
less than 1 for noncarcinogens.
Cleanup goals under CERCLA
• Cleanup goals may be higher than MCLs if the aquifer is
not useable for drinking
(1) Aquifers cannot supply drinking water to a well or spring
sufficient for the needs of an average family;
(2) Ground waters are saline (more than 10g/L total dissolved
solids)
(3) Aquifers are otherwise contaminated from other sources
beyond restoration using reasonable techniques.
(4) If the goals are based on protecting a surface water body.
Cleanup goals under CERCLA
• Cleanup goals may be lower than MCLs for individual
contaminants.
(1) if multiple contaminants are present and the cumulative
risk from all of them exceeds 10-4 for carcinogens or
hazard index of 1 for noncarcinogens.
(2) if the state in which the site is located has state-mandated
MCLs or cleanup standards lower than the federals MCLs.
Cleanup goals under CERCLA
• Cleanup goals may be lower than MCLs for individual
contaminants.
(1) if multiple contaminants are present and the cumulative
risk from all of them exceeds 10-4 for carcinogens or
hazard index of 1 for noncarcinogens.
(2) if the state in which the site is located has state-mandated
MCLs or cleanup standards lower than the federals MCLs.
• Under CERCLA, the EPA may waive health-based cleanup
requirements where achieving them is “technically
impracticable from an engineering perspective” =>
However, the EPA has been criticized for making minimum
use of CERCLA’s statutory waiver provisions.
Cleanup goals under RCRA
• Corrective Action Rule.
(1) No requirement to meet ARARs from other laws.
(2) Generally more flexible than the CERCLA in allowing
cleanup goals other than MCLs.
(3) Alternate concentration limit (ACL) in place of drinking
water
(4) Nevertheless, the US EPA intends that RCRA and
CERCLA should establish a consistent approach for
ground water cleanup. => Therefore, under RCRA the EPA
generally sets cleanup levels at MCLs.
Alternative Cleanup Goals
Resource Use
Partially
restricted
Unrestricted
Complete Cleanup to Cleanup to
healthcleanup background
level or
based
detection limit standards
Cleanup to
capabilities
of current
technology
Cleanup to
allow
nonpotable
uses (i.e.,
irrigation,
recreation)
Restricted
Containment
Alternative Cleanup Goals
Resource Use
Partially
restricted
Unrestricted
Complete Cleanup to Cleanup to
healthcleanup background
level or
based
detection limit standards
Cleanup to
capabilities
of current
technology
Cleanup to
allow
nonpotable
uses (i.e.,
irrigation,
recreation)
Restricted
Containment
DISCUSSION: What would be the impacts of this
relaxed goals in ENVIRONMENTAL INDUSTRY?
Risk is Probability
• Known to cause health problems to most
of people.
• Known to not cause health problems to
most of people
• Uncertain that a chemical is causing any
health problems.
• Which case is the “ultimate evil”?
Risk Assessment
• Epidemiologic and animal studies provide
information about the types of health problems
that may occur from contamination but they may
be insufficient to determine the likelihood that
health problems will occur in a given exposed
pollutions.
• To determine this likelihood, environmental
regulators use a process known as risk
assessment.
Basic steps in risk assessment
• Hazard identification: based upon the
observations from epidemiologic and toxicologic
studies.
• Dose-response evaluation: based upon
information extrapolated from high to low
contaminant dose, small to large animals, and
animals to humans.
• Exposure evaluation: field characterization of
contamination and the population.
• Risk characterization: integration of information
on the above factors.
환경위해성평가
• Risk Assessment
- 서론
- 위해성 평가의 요소
- Hazard Identification (위험성 판별)
- Dose-Response Assessment (용량-반응 평가)
- Human Exposure Assessment (인체노출평가)
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Introduction
• 미국 1980년대에 환경위해성평가가 환경정책에
반영되기 시작하였다.
• 이러한 정책은 국민들이 환경위험에 대해서 경각심을
각기 시작했기 때문이다. (Rachael Carson, “Silent
Spring”; Orange Agents for Vietnam War etc.)
• 위해성 평가 (Risk Assessment): 노출과 보건/건강 간의
상관관계를 평가하기 위한 자료 수집과 분석 (과학적 관점)
• 위해성 관리 (Risk Management): 위해성 평가에
근거해서 국가적 자원을 국민보건에 사용하는 것을
결정하는 의사결정과 행정적 집행 (정책적 관점)
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Perspectives on Risks
• Risk (위해성)은 어떤 독성물질에 의해서 어떤 사람이
병이 걸리거나 심하면 죽을 수 있는 가능성 (probability)
• Ex. 일년 사망자 중 암으로 죽을 확률
• Ex. 일년 사망자 중 교통사고로 죽을 확률
• 생물학적, 활동 및 습관 등 개인적인 차이가 많다.
• When risks are based on models, there are generally
very large uncertainties in the estimates.
Perception on Risk
• 노출위험에 처한 본인의 위해성을 알고 있는
경우에 비해서, 노출위험에 의한 위해성에 대해서
신뢰성 있는 정보가 없을때 더 위해하다고 느낌.
• 예) 주유소 주면에서 살면 벤젠에 의한 발암율이
얼마인지 아는 경우에 비해서, 원자력 발전소
주면에서 살면 발생할 위해성에 대해서 모른 경우
더 불안해 함.
Risk Assessment
Causally linked
to particular
Health effects?
How much of dose
cause adverse
health effect?
Who will be exposed to
the toxicants? (size and
nature of populations)
Integration of the above
three steps to determine
the magnitude of the
public-health problem
Hazard Identification
Goal: 관심대상 물질이 우리 인체에
유해한가를 밝히는 것 (독성학적 관점)
Pathways of Toxicant into Human Body:
1. 음식과 물을 먹고 마시는 것을 통해서
2. 호흡을 통해서
3. 피부와 신체외부기관을 통해서
Organ-Specific Toxicity (see =>)
Side Effects by Toxic Chemicals
1. 중금속은 췌장/간 파괴 => 전신
2. 일산화탄소와 질산성질소는 혈액내
산소공급 방해 => 전신
3. 담배연기, 미세먼지 등이 허파에 문제
(나노입자의 신규문제)
4. 피부는 다양한 화학물질에 반응 (아토피)
The circulatory system and nomenclature of toxic
effects: hepatotoxicity (liver), nephrotoxicity (kidneys),
pulmonotoxicity (lungs), hematotoxicity (blood).
[Source: Based on James, 1985]
Fate of toxicants in the body
Fate of chemical toxicants in the body (Source: Environ. 1988)
Hazard Identification
•
•
•
•
급성독성 파악 Acute Toxicity
유전자돌연변이 Mutagenesis
발암성 진단 Carcinogenesis
세균-동물 독성실험 Toxicity Testing in
Animals
• 인체독성실험 Human Studies
• 발암물질 가능성 가중치 Weight-ofEvidence Categories for Potential
Carcinogens
Acute (급성) Toxicity
•
Philippus Aureolus Theophrastus Bombastus von Hohenheim-Paracelsus,
“화학물질의 주입 양에 따라서 독인지 약인지가 결정된다”.
Mutagenesis
DNA
(deoxyribonucleic acid)
Carcinogens
Teratogens
Possible consequences of a mutagenic event in somatic and germinal cells
Health Risks of Contaminated
Ground Water
•Animal Studies
•Epidemiologic Studies
Animal Studies
• Provide estimates of the long-term human health effects of
environmental contaminants based on the response of
animals to large doses of the contaminant over relatively
short time periods.
• Regulators often must reply on animal studies.
• Essential to a preventive approach to protecting public
health.
Toxicity Testing in Animal
1. 급성독성분석
2. 화학적 구조분석
3. 박테리아 독성분석
(Ames mutagenicity assays)
4. 동물기관을 이용한 독성분석
5. 동물을 이용한 독성분석
(chronic carcinogenesis bioassay)
- 두 종이상의 쥐를 사용할 것
- 최소 수컷 50, 암컷 50을 사용할 것
- 최소 두 Dose 수준을 사용할 것
(max. tolerant dose [MTD] included)
•LD50: lethal dose for 50% of the test population of the most
sensitive species studied.
•No observed effects (NOEL) at any biologically significant end
point = LOEL (Lowest Observed Effects Level) / 10 (uncertainty
factor)
Extrapolating to Humans
Assumption: humans can be 10 times more sensitive than
the most sensitive study species
Uncertainty Factor (UF) <1000
-Uncertainty of the study
-Intraspecies variation
-Interspecies variation (2-3 fold in general)
-10 might be conservative.
-Extrapolating from an acute or subchronic dose range to a chronic
dose.
Reference Dose (RfD): Permissible exposure levels.
RfD = NOEL/UF
Extrapolations from High Doses to Low Doses
고농도의 동물실험결과를 저농도 노출의 인체에 적용하는 것은 매우 힘든
일이고, 사실상 과학적으로 타당성을 찾기 힘들다.
이러한 외삽을 하는 것은 과학적이라기
보다는 정책적 관점과 필요에 의한 것.
많이 사용하는 외삽모델.
1) one-hit model: P(d) = 1 – exp(-q0 – q1d)
P(d): risk (probability)
as a function of dose (d)
d: dose
q0, q1: fitting parameters
2) Multistage model: P(d) =1-exp(-q0-q1d-q2d^2-qnd^n)
3) Linearized multistage model (US EPA)
Hypothetical
dose-response curves
Shortcomings of Animal Studies
• Must extrapolate effect observed in animals that are
administered large doses of the contaminant to humans who
will most likely receive much smaller does)
• Different species may metabolize chemicals in different
ways and therefore may be affected differently by chemical
exposure.
•The current animal studies focus on the effect of single
chemical rather than the effects of mixed chemicals.
Epidemiologic Studies
• Determine health effects by examining specific
populations exposed to the contaminants (either
occupational groups or residents living near
contaminated sites.)
Limitations of Epidemiologic Studies
• Limitations
- Uncertain exposure
- Latency
- Small size of study population
- Inadequate control over comparison groups
- Uncertain health effects of the contaminant
- Presence of contaminant mixtures
- Confounding factors and sources of bias
Human Studies
고농도와 동물실험의 경우는 인간과 인간에 노출된 저농도의 오염노출의
위해성과는 다른 것임. 이를 위해서 인간을 대상으로 한 실증결과가 필요
인간실증자료: (1) 오염누출사고 지역
(2) 역학조사
- Relative risk = [a/(a+b)] / [c/(c+d)]
- Attributable risk = [a/(a+b)] - [c/(c+d)]
- Odds ratio = ad/bc when its value is 1.0
Carcinogenesis (발암성)
• 인류의 최대의 적: 암
• 초기단계: 독성물질이 DNA를 변형시켜서 조절이
되지 않는 세포의 성장이 시작하는 단계.
• 발전단계: 유전적 변형이 생긴 세포가 자라서 혹을
형성하는 단계.
• Metastasis: 암 혹이 몸의 다른 부위로 퍼지는 단계.
Evidence of carcinogenicity
•Evidence in humans from epidemiological
studies
•Evidence in short term in vitro tests
•Strength of evidence from animal toxicity
studies.
•Type of tumor and how many (symptom and
population toxicology)
•Mechanism of action
Dose-Response Assessment
Hypothetical dose-response curves
Weight-of-Evidence Categories for
Potential Carcinogens (US EPA)
Group A (Human Carcinogen): 신빙성있는 역학조사 결과, 인체 발암과 노출이 높은
상관성을 보이는 화학물질.
Group B (Probable Human Carcinogen): 이는 두 그룹으로 구분됨. B1
역학자료는 다소 부족하나 발암 가능성을 보이는 경우; B2 역학자료는
발암가능성을 제시에 제한적이나 동물독성분석결과가 발암 증거를 제시하는 경우.
Group C (Possible Human Carcinogen): 발암성에 대한 동물독성증거가
제한적이고 인체독성증거가 전무한 화학물질.
Group D (Not Classified):동물과 인체에 대한 적절한 발암성 근거가 없는 화학물질.
Group E (Evidence of Noncarcinogenicity): 두 종이상의 동물실험결과와
역학조사결과 발암성이 없다고 알려진 화학물질.
Potency Factor for Carcinogens
The potency factor (PF) is the slope of the dose-response curve. It can
also be thought of as the risk that corresponds to a chronic daily intake of
1 mg/kg-day.
Incremental lifetime cancer risk
PF=
Chronic daily intake [CDI](mg/kg-day)
PF values can be found in an EPA database
on toxic substances called
the Integrated Risk Information System (IRIS).
CDI (mg/kg-day) = Ave. daily dose (mg/day)/Body weight (kg)
The Reference Dose for Noncarcinogenic Effects
LOEL: the lowest-observed-effect level
NOEL: no-observed-effect level
NOAELs: no-observed-adverse-effect levels
RfD: reference dose (acceptable daily intake [ADI])
The Hazard Index for Noncarcinogenic Effects
Average daily dose during exposure period (mg/kg-day)
Hazard quotient =
RfD
(for individual chemical)
Hazard index = Sum of Hazard quotients for all the toxicants
in environment
Human Exposure Assessment
Bioconcentration and Contaminant degradation
Risk Characterization
위해성 특성화에 필요한 정보들 (미국 한림원 제안 사항, 1983)
건강에 미치는 영향에 대한 분석결과의 신뢰성에 대한 정보
생물학적 불확실성과 기원에 대한 정보
독성에 대한 측정방법에 대한 정보?
정량적으로 평가되는 독성요인들은 어떤 것이 있는가?
의사결정에 불확실성이 고려되는 방식은?
어떠한 dose-response assessments와 exposure assessments
방법이 사용되는가?
7. 어떠한 대상인구가 위해성관리에 우선적으로 고려되야 하는가?
8. 대상 위해성을 구체적으로 어떠한 용어로 표현할 것인가?
1.
2.
3.
4.
5.
6.
Uncertainty in Risk Assessment
• Existing evidence is insufficient to provide clear
conclusions about the level of health risk posed
by ground water and soil contamination.
• Nevertheless, the absence of documentation of
health risks cannot be used as proof that
exposure and adverse health effect have not
occurred.
• Given the scientific uncertainties associated
with epidemiology and risk assessment, public
policy makers should err on the side of caution
in setting ground water cleanup goals.
Ecological Risks of Groundwater
Contamination
• At the Munisport landfill in FL, the EPA required
a $6.2 million remedial action because of its
impact on aqueous organisms (because of high
salinity, the health-based standards were not
applied.)
• Impacts on Organisms in Groundwater
• Impacts on Terrestrial Plants
Economics of Groundwater Cleanup
Policy stringency
Removal %
P resen t W o rth in D o lla rs
Remediation method dependent
6000000
6000000
5000000
5000000
4000000
P resent 4000000
W orth in 3000000
D ollars 2000000
1000000
3000000
2000000
90% rem oval
99.9% rem oval
1000000
0
0
1
2
3 4 5 6 7 8
R etardation Factor
0
In situ
conventional
biorem ediation pum p-and-treat
9 10
90 % rem oval 99 % rem oval
The Complexity of Selecting Cleanup Goals
Purposes for use
of ground water
GW remediation
technology
Regulation policy
GW
Cleanup
Goals
Risk Assessment
(human health)
Economics
Ecological Risk
Assessment