ERF of methylmercury

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Question

What is the exposure-response function (ERF) of methyl mercury on several health endpoints such as intelligence quotient and lifetime risk of myocardial infarction after prenatal or long-term adult exposure, respectively?

Answer

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Rationale

Exposure-response of MeHg intake for MI risk in adults is indexed by variable age. It applies to the last two age categories.

Data

ERF of methylmercury(-)
ObsExposure agentResponseExposureExposure unitER functionScalingThresholdERFDescription
1MeHgLoss in child's IQ pointsThrough placenta as maternal MeHg concentration in hairug /gERSNone00.7 (0 - 1.5)
2MeHgLoss in child's IQ pointsMaternal ingested intakeµg /kg /dERSBW06.533 (0 - 14)Converted from the row above assuming linearity
ERF publications
ERF data as described in original articles
Exposure agent Trait Response metric Exposure route Exposure metric Exposure unit ERF parameter Threshold ERF Description
MeHg Childhood intelligence IQ change Placenta Maternal MeHg concentration in hair ug /g ERS 0 -1.5;-0.7;0

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 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, and they use triangular distribution. R↻

According to Health Canada[2], 14 ppm in the hair corresponds to 1.5 µg/kg/d intake of methylmercury. Assuming linearity, the ERF can be converted to

-0.7 \frac{IQp}{\mu g/g} \frac{14 \mu g/g}{1.5 \mu g/kg/d} = -6.533 \frac{IQp}{\mu g/kg/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.[3] R↻


Conversion 2:

Another conversion from MeHg hair concentration into dietary MeHg intake is proposed by the U.S.EPA [4]. 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


were:

  • Concentration_MeHg_Hair is the hair MeHg concentration,
  • b is the elimination rate from blood (assumed 0.014[4]),
  • V is the blood volume (assumed 5 L[4]),
  • f is the fraction of absorbed MeHg that is distributed to the blood (assumed 0.059[4]),
  • A is the fraction of ingested MeHg that is absorbed from GI tract (assumed 0.95[4]),
  • 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).

Jyrki K. Virtanen, Tiina H. Rissanen, Sari Voutilainen, Tomi-Pekka Tuomainen. Mercury as a risk factor for cardiovascular diseases. Journal of Nutritional Biochemistry 18 (2007) 75–85. Beneris:media:Virtanen_JNutrBiochem_2007_HgandCVD.pdf

Unit

Conversion 1
IQ points / 1 µg/g increase in maternal hair
Conversion 2
IQ points/(µg/(kg bw*day))

Calculations

+ Show code

Conversion 1 (Analytica)
triangular(-1.5,-0.7,0)*Blood_to_hair
Conversion 2
triangular(-1.5,-0.7,0)*(0.8007*BW*250*0.001)

See also

References

  1. Cohen JT, Bellinger DC, Shaywitz BA. A quantitative analysis of prenatal methyl mercury exposure and cognitive development. Am J Prev Med. 2005 Nov;29(4):353-65. [1]
  2. Olli Leino: Fish consumption: human health effects and decision making. National Institute for Health and Welfare, Research 120/2014. Dissertation.
  3. Methyl mercury: Bidone et al. (2004)
  4. 4.0 4.1 4.2 4.3 4.4 EPA (IRIS), 2001. http://www.epa.gov/iris/subst/0073.htm