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Systems Safetyー Environmental Risk Assessment ー

Kazuo FURUTA (RERC)

Toxic substances

Chemicalsn Arsenic, hydrocyanic acid, NOx, SOx, etc.n Natural poisons (mushroom, snake, insect, etc.)n Pesticide (insecticide, herbicide, etc.)n Dioxin, endocrine disruptor, etc.

Heavy metals and mineralsn Lead, mercury, cadmium, etc.n Asbestos

Radioactivity

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Risk assessment of toxics

Assessment of releasen Location and amount of release

Transportation analysisn Transportation of toxics in environment

Assessment of exposure leveln Exposure of an organism to toxics

Assessment of effectsn Adverse health effects by toxics

Diffusion of matter

A matter is transported from the high-density site to the low-density site by random motion of molecules

Fick’s law

D : Diffusion coefficient

High-d. Low-d.

A

AA

CDx

CDJ

grad−=∂

∂−=

AJ

(1-D)

(3-D)

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Diffusion equation

∂∂

∂=

∂∂

∂∂

+

∂∂

∂=

∂∂

∂

∂+

∂∂

+∂

∂=

∂∂

rCr

rrD

tC

zCD

rCr

rrD

tC

zC

yC

xCD

tC

AA

AAA

AAAA

22

2

2

2

2

2

2

2

2

1

1

C0

AA CD

tC 2∇=∂

∂

Cartesian

Cylindrical

Polar

Chemical reaction rate

ktAAAAk

tA

0

02

1][][][

+=⇒−=

∂∂　

C0

General form of chemical reaction rate

First-order reaction in terms of A

Second-order reaction in terms of A

)exp(][][][0 ktAAAk

tA

−=⇒−=∂

∂　

Lba BAk ][][=ν

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Convection-diffusion model

1-D convection-diffusion model

1-D convection-diffusion-reaction model

zCv

zCD

tC

vCzCDvC

zCD

tCz

zzzavg

∂∂

−∂

∂=

∂∂

+

∂∂

−−

+

∂∂

−=

∂∂

∆∆+

2

2

kCzCv

zCD

tC

−∂∂

−∂

∂=

∂∂

2

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Environmental chemodynamics

Estimation of transportation paths of toxics from the sources to the living environment

Evaluation of the densities of toxics in the air, water, foods, and soil that people take or make contact with

Evaluation of the intake of toxics considering the physiological features and the lifestylen Oral intake, suction, skin absorption

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Example scenario of radioactivity transportation by groundwater

地下水位

海への移行

廃棄物充てん土壌

降雨の廃棄物層への浸透

降雨による核種の地下水への移行 海

覆土

灌漑 飼育水 飲用

海岸活動者・汚染された土壌からの直接線・汚染された土壌粉塵の吸入

飲料水摂取畜産物摂取

汚染された土壌

農耕作業、農産物摂取者・汚染された土壌からの直接線・汚染された土壌粉塵の吸入・農作物摂取

養殖水産物摂取

養殖水

地下水が利用されている場合

地下水が利用されていない場合

飲料水摂取（低頻度事象）

井戸水利用

海産物摂取

地下水位

海への移行

廃棄物充てん土壌

降雨の廃棄物層への浸透

降雨による核種の地下水への移行 海

覆土

灌漑 飼育水 飲用

海岸活動者・汚染された土壌からの直接線・汚染された土壌粉塵の吸入

飲料水摂取畜産物摂取

汚染された土壌

農耕作業、農産物摂取者・汚染された土壌からの直接線・汚染された土壌粉塵の吸入・農作物摂取

養殖水産物摂取

養殖水

地下水が利用されている場合

地下水が利用されていない場合

飲料水摂取（低頻度事象）

井戸水利用

海産物摂取

Water in useWater

not in use

Accidental intake

well

Groundwater level

Contaminated soil

Drink waterSea foodsMeat & milk

Sea foods

Sea

Irrigation Stock farming Cultivation Drinking

Packingsoil

Cover

Infiltration of rain

Transfer into groundwater

Exposure by farming· Direct irradiation· Suction of soil dust

Exposure by outdoor activities· Direct irradiation· Suction of soil dust

Transfer to sea

Chemodynamics within body

Organs

Gut (out)Gut (in)

Muscle

Liver

Kidney

Fat

Skin

Blood Blood

Suction

Oral intake Excretion

ExcretionMetabolism

Box model

Lung (in)Lung (out)

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Types of toxicity

Acute toxicityn Adverse effects caused by single exposure or

multiple exposures in a short time (<24hrs)n Medium lethal dose (LD50)w The dose required to kill half the tested populationw The mass of substance per unit mass of subject (mg/kg)

Semi-acute toxicity (1d~1yr)

Chronic toxicityn Adverse effects caused by repeated exposures

over a longer period (1yr<)

Radiation effects

Types of radiationn α-ray, β-ray, γ-ray, …

Measures of radioactivity and radiationn Radioactivity (Bq), absorbed dose (Gy), dose

equivalent (Sv)

Adverse effects of radiation exposureWhat depends

on dose Threshold Principal effects

Probabilistic Probability of adverse effects (no) Cancer,

genetic disorder

Deterministic Degree of adverse effects yes Cataract, burn,

infertility

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in vivo / in vitro testing

in vivo testingn Experiment using animals (mice)n Toxicity evaluation of environment

in vitro testingn Experiment using living tissue or cellsn Examination of poisoning mechanism

Issues with experimental methodsn Cost effectivenessn Reliability of outcomesn Extrapolation of outcomes to humans

Epistemological study

Cohort studyn Two groups of samples, exposed and unexposed,

are followed over time on manifestation of effects.

Case-control studyn Two groups of samples, with and without effects,

are examined on the past exposure history.

Cross-sectional studyn Samples are examined on both the present

adverse effects and the past exposure history.

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Data processing in epistemology

Risk ratio (Cohort study)R = [a/(a+b)] / [c/(c+d)]

Odds ratio (Case-control study)φ = (a/c) / (b/d)

Effects No effects

Exposed a b

Non-exposed c d

Bias in epistemology

Bias: Factors that impair the validityn Selection bias

– Samples were selected inappropriately.

n Information bias– The collected information were inappropriate.

n Confounding– The groups to be compared are not equivalent in terms

of some factors other than exposure.

Statistical uncertainty

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Dose-response relationship

Exposure Exposure

Deg

ree

of d

amag

e

Prob

abili

ty o

f da

mag

e

0 0

100

Non-cancer effects Cancer or genetic effects

Threshold

100

Toxicity measures with threshold

No Observable Effect Level (NOEL)n Highest dose with no observable effects

Lowest Observable Effect Level (LOEL)n Lowest dose with any observable effect

No Observable Adverse Effect Level (NOAEL)n Highest dose with no observable adverse effects

Lowest Observable Adverse Effect Level (LOAEL)n Lowest dose with any observable adverse effect

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Non-cancer risk

Acceptable Daily Intake (ADI)ADI = NOAEL / Safety factor (10)

Tolerable Daily Intake (TDI)n Intake limit of toxic substance with no benefits

Hazard Ratio (HR)HR = Exposure level / AID or Exposure level / TDI

Hazard Index (HI)n When more than one hazards exist

HI = ΣHRi

Carcinogenesis measures

Cancer unit riskn Increase of cancer risk per unit density of

carcinogen for lifetime intake

Cancer potencyn Dose of carcinogen that yields 5% of

cancer probability

Cancer slope factorn Increase of cancer risk per mg of

carcinogen intake / kg body weight-day

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Environmental risk

Endpointn An event that people want to avoidn Relevant to avoid adverse effects to environmentn Measurable and predictablen Sensitive enough for risk management

Selection of endpointn Which level should be focused on?

Individual, group, public, ecosystem

Allowable risk limit

Absolute risk limitn The risks that exceed the particular limit

must be reduced.Ex. Cancer risk of drink water < 10-5/lifetime

Risk-benefit tradeoffn The risks with a low benefit per unit risk

are the first ones to be reduced. n The risks with a very high benefit per unit

risk should not be reduced.

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Benefit-risk ratio (B/R)

Unit of riskn Death of one person (B/R = price of life)n Reduction of lifetime (B/R = price of lifetime)

reduced] be to [Riskrisk] the reducingfor requiredCost

ortaken] be to Risk

risk the takingby obtainableBenefit

[

[][

=

=

RB

RB

Example of risk-benefit tradeoff

Regulatory optionsB/R

(mill.yen/man・yr）Ban on Chlordane (termiticide)Ban on mercury in soda productionShift to mercury-free battery cellsRegulation of benzene in gasolineRegulation of NOX in car exhaustRegulation of dioxin from incinerator

Urgent actionPermanent action

4505,700

2202,300

860

791,500

R: 1yr of LLE

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Cost-benefit analysis

Comparison of B/R with the price of lifen Evaluation from wage difference between

dangerous and undangerous jobsn WTP (Willing To Pay) obtained through CVM

(Contingency Valuation Method)

Points to be discussedn Consideration of vulnerable groupsn Difference between voluntary and involuntary risksn Uncertainties in risk assessment