Risk assessment of mercury exposure through fish consumption by the riverside people in the Madeira Basin, Amazon, 1991.

Aquatic food chain mercury pollution is one of the consequences of the gold rush in the Amazon, which started in the late 1970s. This paper addresses the risks of methylmercury (MeHg) toxicity by a riverside population of heavy fish eaters along the Madeira river, in the Amazon, based on their hair mercury (Hg) concentration. Given the vulnerability of the developing nervous system, NOEL/LOEL values were used based on prenatal (LOELp = 0.7 microgram/ kg bw), and adult and childhood (LOELa = 3 micrograms/kg bw) Hg exposures. Based on hair Hg concentrations, we observed that approximately 95% of infants were at risk of absorbing Hg through the previous placental exposure, and/or by ingesting Hg from mother's milk, and/or fish consumption, at a level as great as the LOELp. The hazard quotient derived from the LOELp for neurobehavioral effects was 64 based on an estimated mean Hg daily intake of 4.5 micrograms/kg bw. Approximately 45% of the mothers of the infants and other women of child bearing age were at risk of ingesting Hg at a level equivalent to the LOELp. This also translates into a derived hazard quotient for neurobehavioral effects of 17 for all potential mothers in the population. The non-infant population at the highest risk was fish-eating children under 5 years old. This sub-population had a mean estimated Hg daily intake of 6.4 micrograms/kg bw. This resulted in a probability that almost 60% of this sub-population ingested Hg at a level equivalent to the LOELa or higher. For this sub-population, there was a hazard quotient of 21. These data strongly indicate that the young children of this riverside fish-eating population may be ingesting Hg doses that have been correlated with neurological damage from Hg poisoning.

[Exposure to organic mercury in riparian populations on the Upper Madeira river, Rondonia, Brazil, 1991: preliminary results]. / Exposição ao mercúrio orgânico em populações Ribeirinhas do Alto Madeira, Rondônia, 1991: resultados preliminares.

This study analyzes mercury concentration in hair samples obtained from the population living in the Upper Madeira River basin, Rondonia. Out of 311 hair samples analyzed, 51% (n=158) had a mercury concentration of over 10 ppm. The wide variability of mercury concentration is well-illustrated by a family in which there were 5 cases with the highest mercury concentrations (90.6 to 303.1 ppm), while in another 5 household members, the concentration ranged from 7.0 to 13.3 ppm. Special attention must be paid to women in the childbearing age, since the fetus is more vulnerable to lower mercury concentrations. 53% (n=37) females in the reproductive age bracket (age group 4) displayed a mercury concentration above 10 ppm.

Segmental hair mercury evaluation of a single family along the upper Madeira basin, Brazilian Amazon.

Mercury pollution (MeHg) up the aquatic food chains in the Amazonian ecosystems has been a major concern in environmental health. Riverside people (ribeirinhos) along the Upper Madeira river are heavy fish eaters. Hair is the best biomarker for MeHg exposure. By assuming a constant hair growth rate, it is possible to evaluate a temporal profile of Hg exposure over the recent defined past. In this paper we present the segmental total hair Hg concentrations from a single family from which some of the 10 persons investigated had high hair Hg concentrations (peak of 339 ppm). We also presented the hair MeHg content from 4 out of the 10 family members investigated. There was a wide variation in total hair Hg concentrations (8 to 339 ppm) among these individuals, who were mostly sharing their meals; there was also a wide variation in total Hg concentrations in the same individual over time (136 to 274 ppm). Hg speciation showed a mean and standard deviation in the MeHg content of 62% and 6%, respectively. The wide variation in total hair Hg concentration strongly indicated that it is possible to mitigate critical Hg exposure levels by conducting a fish advisory.

Longitudinal hair mercury concentration in riverside mothers along the Upper Madeira river (Brazil).

Mercury releases from gold mining occurred during the 1980s in the Upper Madeira river, a Southern tributary of the Amazon. Downstream from these areas, riverside residents rely on fish consumption for subsistence. In July of 1993, hair samples were collected for mercury analysis from a group of mothers and their infants and one pregnant woman. By assuming a constant rate of hair growth (1.1 cm per month), a temporal profile of the methylmercury exposure was determined for the previous 2 to 3 years. The length of hair segments corresponded to hair growth during pregnancy and the subsequent breastfeeding periods. During all periods, hair mercury concentrations in six mothers were in the range of 4.5-26.8 ppm, slightly lower than those of their infants (8.2-28.4 ppm). Further segmental analyses of hair mercury from another six mothers showed concentrations in the range of 12.2-41.0 ppm during the three trimesters of pregnancy and 4.0-33.5 ppm during breast feeding-slightly lower than their infants (11.6-50.4 ppm). Another four mothers showed hair mercury concentrations in the range of 21. 3-84.4 ppm.

Linear regression models of methyl mercury exposure during prenatal and early postnatal life among riverside people along the upper Madeira river, Amazon.

This research is focused on prenatal and early postnatal mercury (Hg) exposure among the riverside people along the Upper Madeira river in the Amazon. Linear regression models were developed to predict the hair Hg concentration in infants. The independent variables included in the model of Group 1 (87 pairs of mothers and their infants) were the average maternal hair Hg concentration and maternal age. Group 2 (31 pairs) included maternal segmental hair Hg concentrations. For the segmental hair Hg analysis over time, it was assumed that hair grows at a rate of 11 cm per month. Thus, information on the timing of the dates of pregnancy and breast feeding from the birth history was used to cut the hair strands into segments, making them correspond to the mother's reproductive stage of life (31 pairs of mothers and their infants). Breast milk Hg concentration results were included with segmental and average maternal hair Hg concentration values (22 and 44 pairs of mothers and their infants, respectively). The models including the breast milk Hg concentration indicated that 61 and 55% of the variability of the infant hair Hg concentrations were due to the independent variables: segmental maternal hair Hg with breast milk Hg and average maternal hair Hg with breast milk Hg, respectively. The regression coefficients were in the range of 0.19 to 0.90, and P values were in the range of 0.0001 to 0.1490. Further recommendations include fish advisories to prevent critical Hg exposures during reproductive life and investigation of neurobehavioral performance of this study population.

Fish consumption, fish lore, and mercury pollution--risk communication for the Madeira River people.

Fish is an important food resource in Amazonian aquatic ecosystems. There is a strong cultural background regarding fish consumption (fish lore) among indigenous people in the Amazon. Mercury (Hg) ingestion through fish consumption has been a major route of Hg exposure among the riverside people along the Upper Madeira River. In this paper a diet questionnaire was used to identify patterns of fish consumption. The amount of fish consumed during the dry season and Hg levels in fish were combined to estimate Hg ingestion. Using as guidance hair Hg levels below 5 and 10 ppm as acceptable to protect the fetus and adult, respectively, along with an average daily fish consumption of 243 g per capita, we estimated the maximum acceptable number of fish meals per week for different fish species. Based on this analysis, it is suggested that there is a need to address risk communication for this exposed population in the context of health in terms of a fish advisory. For the fish advisory it is necessary to recommend to fish consumers, fishermen, and fish sellers an acceptable number of fish meals to be consumed according to species.

Effects of uncertainties on exposure estimates to methylmercury: a Monte Carlo analysis of exposure biomarkers versus dietary recall estimation.

This article presents a general model for estimating population heterogeneity and "lack of knowledge" uncertainty in methylmercury (MeHg) exposure assessments using two-dimensional Monte Carlo analysis. Using data from fish-consuming populations in Bangladesh, Brazil, Sweden, and the United Kingdom, predictive model estimates of dietary MeHg exposures were compared against those derived from biomarkers (i.e., [Hg]hair and [Hg]blood). By disaggregating parameter uncertainty into components (i.e., population heterogeneity, measurement error, recall error, and sampling error) estimates were obtained of the contribution of each component to the overall uncertainty. Steady-state diet:hair and diet:blood MeHg exposure ratios were estimated for each population and were used to develop distributions useful for conducting biomarker-based probabilistic assessments of MeHg exposure. The 5th and 95th percentile modeled MeHg exposure estimates around mean population exposure from each of the four study populations are presented to demonstrate lack of knowledge uncertainty about a best estimate for a true mean. Results from a U.K. study population showed that a predictive dietary model resulted in a 74% lower lack of knowledge uncertainty around a central mean estimate relative to a hair biomarker model, and also in a 31% lower lack of knowledge uncertainty around central mean estimate relative to a blood biomarker model. Similar results were obtained for the Brazil and Bangladesh populations. Such analyses, used here to evaluate alternative models of dietary MeHg exposure, can be used to refine exposure instruments, improve information used in site management and remediation decision making, and identify sources of uncertainty in risk estimates.