ERF of methyl mercury on intelligence quotient: Difference between revisions

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{{Variable|Exposure-response functions}}
[[Category:Exposure-response functions]]
[[Category:Heavy metals]]
{{Variable|moderator=Olli}}


== Scope ==
== 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).
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 ==  
== Definition ==  


=== Causality ===
=== Data ===
List of parent variables:
 
*[[Body weight in Finland]]
Study by Cohen et al<ref name="cohenMMVa">Methyl mercury: Cohen et al 2005a</ref> 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 <ref>[[User:Jouni]] 9 Feb 2008</ref>. {{disclink|Author judgement about the chosen distribution}}
 


=== Data ===
'''Conversion 1:


'''Actual content'''
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.<ref>Methyl mercury: Bidone et al. (2004)</ref> {{disclink|Toxicologicy of methylmercury}}


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).


'''Conversion 2:


'''Narrative description'''
Another conversion from MeHg hair concentration into dietary MeHg intake is proposed by EPA <ref name="EPA"> EPA (IRIS), 2001. http://www.epa.gov/iris/subst/0073.htm </ref>. 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


Every 1 ug/g of methylmercury in mothers hair decreases IQ of a child by 0.7 points. Study by Cohen et al<ref name="cohenMMVa">Methyl mercury: Cohen et al 2005a</ref> 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.<ref name="cohenMMVa"/>
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))


A triangular distribution with parameters: min = 0, mode = 0.7 and max = 1.5 was created. Distribution by author judgement. {{disclink|Author judgement about the chosen distribution}}
were:
* Concentration_MeHg_Hair is the hair MeHg concentration,
* b is the elimination rate from blood (assumed 0.014<ref name ="EPA" />),
* V is the blood volume (assumed 5 L<ref name ="EPA" />),
* f is the fraction of absorbed MeHg that is distributed to the blood (assumed 0.059<ref name ="EPA" />),
* A is the fraction of ingested MeHg that is absorbed from GI tract (assumed 0.95<ref name ="EPA" />),
* 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.


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.<ref>Methyl mercury: Bidone_et_al(2004)</ref> {{disclink|Toxicologicy of methylmercury}}
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===


Another conversion from MeHg hair concentration into dietary MeHg intake is proposed by EPA <ref name="EPA"> EPA (IRIS), 2001. http://www.epa.gov/iris/subst/0073.htm </ref>. 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
List of parent variables:
*[[Body weight in Finland]]


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))
== Unit ==


were: <br>
;Conversion 1: IQ points / 1 µg/g increase in maternal hair
- Concentration_MeHg_Hair is the hair MeHg concentration,<br>
- b is the elimination rate from blood (assumed 0.014<ref name ="EPA" />),<br>
- V is the blood volume (assumed 5L<ref name ="EPA" />),<br>
- f is the fraction of absorbed MeHg that is distributed to the blood (assumed 0.059<ref name ="EPA" />),<br>
- A is the fraction of ingested MeHg that is absorbed from GI tract (assumed 0.95<ref name ="EPA" />),<br>
- BW is the body weight of pregnant woman,<br>
- a is the proportion of daily dietary intake of MeHg by pregnant women that comes from fish (assumed 1=100%),<br>
- 250 is the hair-to-blood Hg concentration ratio.<br>


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).
;Conversion 2: IQ points/(µg/(kg bw*day))


=== Formula ===
=== Formula ===
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Formula used in '''Beneris BBN''': triangular(-1.5,-0.7,0)*(0.8007*BW*250*0.001)
Formula used in '''Beneris BBN''': triangular(-1.5,-0.7,0)*(0.8007*BW*250*0.001)


== Unit ==
== Result ==


IQ points / 1 ug/g increase in maternal hair
NOTE! Conversion 2 was used for the current results.


'''Beneris BBN''': IQ points/ 1(ug/kg bw-day)
{{resultlink}}
 
== Result ==


{{resultlink}}
[[image:ERF of methyl mercury on intelligence quotient.png]]


==References==
==References==


<references/>
<references/>

Revision as of 19:59, 16 September 2009



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[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.

A triangular distribution with parameters: min = 0, mode = 0.7 and max = 1.5 was created. Distribution by author judgement [2]. 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] D↷


Conversion 2:

Another conversion from MeHg hair concentration into dietary MeHg intake is proposed by 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 

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[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).

Dependencies

List of parent variables:

Unit

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

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)

Result

NOTE! Conversion 2 was used for the current results.

{{#opasnet_base_link:Op_en1806}}


References

  1. ↑ Methyl mercury: Cohen et al 2005a
  2. ↑ User:Jouni 9 Feb 2008
  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
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