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
⇤#: Please note that the following new pieces of information have not been considered when writing the page:
- Seychell study: omega-3 blocks the effects of mercury
- EFSA benefit-risk assessment about omega-3 and mercury, press release
- EFSA benefit-risk assessment about omega-3 and mercury --Jouni (talk) 11:51, 26 January 2015 (UTC)
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
| Obs | Exposure agent | Response | Exposure | Exposure unit | ER function | Scaling | Threshold | ERF | Description |
|---|---|---|---|---|---|---|---|---|---|
| 1 | MeHg | Loss in child's IQ points | Through placenta as maternal MeHg concentration in hair | ug /g | ERS | None | 0 | 0.7 (0 - 1.5) | |
| 2 | MeHg | Loss in child's IQ points | Maternal ingested intake | µg /kg /d | ERS | BW | 0 | 6.533 (0 - 14) | Converted from the row above assuming linearity |
- ERF publications
| 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
- Failed to parse (Missing <code>texvc</code> executable. Please see math/README to configure.): -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
- 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
- ↑ 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]
- ↑ Olli Leino: Fish consumption: human health effects and decision making. National Institute for Health and Welfare, Research 120/2014. Dissertation.
- ↑ Methyl mercury: Bidone et al. (2004)
- ↑ 4.0 4.1 4.2 4.3 4.4 EPA (IRIS), 2001. http://www.epa.gov/iris/subst/0073.htm
