ERF of methyl mercury on intelligence quotient

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Scope

What is the exposure-response function (ERF) of methyl mercury on intelligence quotient between exposure to prenatal methyl mercury and intelligence quotient (IQ) score in children?

Definition

Data

Study by Cohen et al finds that prenatal MeHg exposure sufficient to increase the concentration of mercury in maternal hair at parturition by 1 µg/g decreases IQ by 0.7 points. The paper identifies important sources of uncertainty influencing this estimate, concluding that the plausible range of values for this loss is 0 to 1.5 IQ points.

A triangular distribution with parameters: min = 0, mode = 0.7 and max = 1.5 was created. Distribution by author judgement . D↷

Conversion 1:

This variable includes conversion from mercury intake to mercury concentration in hair. Firstly, WHO(1990) suggests the use of a single-compartment model, through which the steady-state Hg concentration in blood (C) in µg/l is related to the average daily dietary intake (d) in µg of Hg, as follows: C = 0.95 * d. Secondly, blood mercury was converted to total hair mercury using a 1:250 ratio (New Zealand and Seychilles Island studies) and an assumption of equivalent maternal and cord levels. D↷

Conversion 2:

Another conversion from MeHg hair concentration into dietary MeHg intake is proposed by EPA . This conversion is used in the Bayesian Belief Network (BBN) model developed for the fish case study in Beneris project. Assuming that the concentration of MeHg in blood is at a steady-state the daily dietary intake of MeHg from fish corresponding to a given hair MeHg concentration can be estimated as

Intake_MeHg_Fish(ug/kg bw-day) = (a*1000*Concentration_MeHg_Hair(ug/g hair)*b(1/day)*V(L blood))/
(250(L blood/kg hair)*A*f*BW(kg bw))

were:

• Concentration_MeHg_Hair is the hair MeHg concentration,
• b is the elimination rate from blood (assumed 0.014),
• V is the blood volume (assumed 5 L),
• f is the fraction of absorbed MeHg that is distributed to the blood (assumed 0.059),
• A is the fraction of ingested MeHg that is absorbed from GI tract (assumed 0.95),
• BW is the body weight of pregnant woman,
• a is the proportion of daily dietary intake of MeHg by pregnant women that comes from fish (assumed 1=100%),
• 250 is the hair-to-blood Hg concentration ratio.

As a result, the ERF of MeHg exposure from fish for the child's IQ can be calculated as a product of ERF of MeHg hair concentration for child's IQ and (A*f*BW*250*0.001)/(b*V).

Dependencies

List of parent variables:

• Body weight in Finland

Unit

Conversion 1

IQ points / 1 µg/g increase in maternal hair

Conversion 2

IQ points/(µg/(kg bw*day))

Formula

Conversion 1 (Analytica)

<Anacode>triangular(-1.5,-0.7,0)*Blood_to_hair</Anacode>

Conversion 2

triangular(-1.5,-0.7,0)*(0.8007*BW*250*0.001)

Result

NOTE! Conversion 2 was used for the current results.

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