ERF of methyl mercury on intelligence quotient
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Scope
ERF of methyl mercury on intelligence quotient describes the quantitative relationship between exposure to (prenatal) methyl mercury exposure and intelligence quotient (IQ) score (in children).
Definition
Causality
List of parent variables:
Data
Actual content
Prenatal MeHg exposure sufficient to increase the concentration of mercury in maternal hair at parturition by 1 ug/g decreases IQ by 0.7 points (min and max 0 and 1.5, respectively).
Narrative description
Every 1 ug/g of methylmercury in mothers hair decreases IQ of a child by 0.7 points. Study by Cohen et al[1] finds that prenatal MeHg exposure sufficient to increase the concentration of mercury in maternal hair at parturition by 1 ug/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.[1]
A triangular distribution with parameters: min = 0, mode = 0.7 and max = 1.5 was created. Distribution by author judgement. D↷
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 ug/l is related to the average daily dietary intake (d) in ug 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.[2] D↷
Another conversion from MeHg hair concentration into dietary MeHg intake is proposed by EPA [3]. 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[3]),
- V is the blood volume (assumed 5L[3]),
- f is the fraction of absorbed MeHg that is distributed to the blood (assumed 0.059[3]),
- A is the fraction of ingested MeHg that is absorbed from GI tract (assumed 0.95[3]),
- 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 concnetration for child's IQ and (A*f*BW*250*0.001)/(b*V).
Formula
Analytica_id:
<Anacode>triangular(-1.5,-0.7,0)*Blood_to_hair</Anacode>
Formula used in Beneris BBN: triangular(-1.5,-0.7,0)*(0.8007*BW*250*0.001)
Unit
IQ points / 1 ug/g increase in maternal hair
Beneris BBN: IQ points/ 1(ug/kg bw-day)
Result
