Exposure Patterns and Long Term Sequelae on Adults and Children in Two Canadian Indigenous Communities Exposed to Methylmercury

Health Canada has been collecting data on Inuit and First Nations' methylmercury (MeHg) levels for 25 years. A national overview has been completed and more focussed analyses have now been initiated. This paper deals with two interdependent analytical components: 1) a longitudinal overview of the two most extensively sampled communities in Canada: Grassy Narrows and Whitedog, the residents of which were exposed to ‘point source’ mercury pollution in the 1970's; 2) fetal and post-natal exposure to mercury in these two communities including an outline of the First Nation MeHg child development pilot project in the two communities. A retrospective analysis of Grassy Narrows and Whitedog shows a decreasing MeHg trend in both communities. In Grassy Narrows the average individual annual peak methylmercury level in blood has decreased significantly, from 23.80 ppb (range 1.50–322.90) in 1976 to 7.5 ppb (1.7–46.7) in 1995 (r=-0.65, p<0.001). In Whitedog the average peak has also decreased significantly, from 12.87 ppb (1.50–172.00) in 1976 to 6.1 ppb (1.7–33.3) in 1995 (r=-0.59, p<0.005). However, behind these positive trends is the reality of two communities still suffering the effects of disrupted lifestyles and socio-cultural damage. A number of cord blood samples, maternal blood samples, and samples from women of child-bearing age from these communities have been in the “risk” group (according to the 1990 WHO guidelines). We are therefore now assessing the long term effects of fetal exposure in the communities. Standard clinical examinations in the past failed to prove abnormalities attributable to methylmercury but did not include subtle neuropsychological development tests. Many of the fetally exposed children are now in secondary school. Therefore, we have initiated a pilot project to assess long term effects of methylmercury exposure on the neuropsychological development of these children whose fetal exposure we know. The pilot child development project which was initiated in 1995 in Grassy Narrows and Whitedog, with community support, includes four main components: i) a school records review, looking at attendance, marks, and atypical behaviour; ii) teachers' questionnaires, targeting child behaviour; iii) an in-depth neuropsychological test battery focussing on subtle factors, such as memory, attention, executive functions, perceptual functions and sensory / motor development; and iv) hair sampling, providing current MeHg levels to correlate with results from the previous sampling and findings from the first three components. An overview of progress is given.     

Mercury exposure in humans through food consumption from the Everglades of Florida

In March 1989, The Florida Department of Health and Rehabilitative Services (HRS) issued a Health Advisory recommending the limited consumption of several fish species caught from the Everglades region of South Florida due to elevated methylmercury (MeHg) levels (average 2–3 ppm in fish meat). There were no reports of clinical MeHg poisoning in humans in Florida, although deaths of Florida panthers were attributed to mercury (Hg). poisoning. This study evaluated the extent of MeHg exposure in persons eating contaminated fish in the Everglades region. Populations at risk were identified including sport fishermen, Everglades Residents and subsistence fishermen. Over 1700 individuals were approached; those who had eaten fish or wildlife from the contaminated areas at least once/month for the prior three months were asked to participate. Three hundred and fifty (350) participants completed a brief questionnaire and provided a hair sample for Hg analysis. In 119 (36%) of individuals with levels above the limits of detection, the mean total Hg in hair was 3.62±3.0μg/g [± standard deviation] with a range of 1.28 – 15.57. The most at risk populations identified with respect to Hg levels were Blacks and men. Although the majority of the participants had fished in the Everglades for many years (>15 years), they reported relatively low intake of fish and had low hair Hg levels compared with similar populations in prior studies of other populations at risk. Although 71% of participants knew of the State Health Advisories concerning ingestion of Hg contaminated fish from the Everglades, this did not change their consumption habits. In addition, Blacks, individuals of lower income and of lower education levels were less likely to know about the Health Advisories. Given recent studies of neurologic effects from relatively low in utero MeHg exposure, the continuation of the Mercury Health Advisories and wildlife monitoring in the Everglades are warranted, especially for women of childbearing age and children. However, public education must be targeted for the populations at risk identified in this study in order to reach these populations more effectively.     

Exposure of James Bay Cree to methylmercury during pregnancy for the years 1983–91

Since 1982 the Cree Board of Health and Social Services of James Bay (Quebec, Canada) has taken samples of hair from Cree men and women in the course of the methylmercury (MeHg) surveillance program. As a measure of foetal exposure, samples of hair of the mother are taken at the beginning of pregnancy and shortly after birth (to determine exposure at birth) and a blood sample is taken from the umbilical cord blood of the newborn. Of the 2360 births between 1983 and 1991, 25% had all three samples taken, but there was not a single sample for 25% of the births. From 1983–1991, the concentrations of mercury (Hg) at the time of conception, at the time of birth and in the umbilical cord have decreased progressively. There is no relationship between Hg in the umbilical cord blood and the weight of the newborn. As is to be expected there is a relationship between the maternal hair concentration at birth and umbilical cord blood Hg concentration at birth. The relationship is the following: Hg cord blood = 8.53+.88xHg maternal blood equivalent {r=0.623, 95% CI(r) [0.770, 0.769] p<0.001}.     

Mercury contents of some greek soils

Mercury contents were determined for horizons or layers of eleven profiles in agricutural areas and three in industrial areas of Greece.Mercury contents were determined for horizons or layers of eleven profiles in agricultural areas and three in industrial areas of Greece.Contents ranged from 25 to 98 ppb in profiles from agricultural areas. No trends in distribution within profiles or among kinds of soils were evident. Moreover, the levels are within the ranges found in uncontaminated soils elsewhere in the world. The contents are therefore considered to be normal background levels for soils of Greece. Amounts of mercury were positively correlated with cation exchange capacity but not with proportions of clay and organic matter.Contents of mercury reached a maximum of 325 ppb in upper layers and had a minimum of 45 ppb in the deeper parts of the profiles from the industrial areas. The greater amounts in the surface layers are attributed to enrichment through industrial activity. The maximum amounts are well above 150 ppb, a level proposed elsewhere as an upper limit for natural backgrounds.     

Mercury Accumulation in Transplanted Hypogymnia Physodes Lichens Downwind of Wisconsin Chlor-Alkali Plant

Emissions of mercury from a chlor-alkali plant in central Wisconsin have raised concern about possible effects on biota in the area. Samples of the lichen Hypogymnia physodes, which no longer grows in the area, were transplanted from a site in northeastern Wisconsin and positioned on plastic stands at varying distances up to 1250 m from the plant and sampled for Hg quarterly for one year to test the hypothesis that Hg would be taken up by the lichens and would decline with distance. Average tissue concentrations were elevated when first sampled at three months and continued to increase at the nearest sites until the study ended after one year. Average concentrations after a year of exposure ranged from 4418 ppb at 250 m from the plant to 403 ppb at 1250 m from the plant. The decrease over distance followed a negative exponential pattern. Background concentrations at a control site in northern Wisconsin averaged 155 ppb.     

Mercury accumulation in transplanted moss and lichens at high elevation sites in Quebec

Mercury deposition was monitored at two mountain sites in Quebec using transplanted lichens and moss. The terricolous lichen species Cladina rangiferina, the epiphytic lichen species Hypogymnia physodes, and the feather moss Pleurozium schreberi were transplanted from a northern Ontario boreal site to the bases and summits of Roundtop Mountain and Mt. Tremblant in southern Quebec. After 12 months, transplants of C. rangiferina sited at the base and summit of Roundtop mountain and the summit of Mt. Tremblant showed a significant increase in mercury concentration over controls (p < 0.05). The largest difference occurred at the summit of Roundtop mountain where mercury concentration was 81.4 ± 10.9 ppb as compared to 45.6 + 10.6 ppb at the control site. No significant increases in mercury concentration in P. schreberi were seen after 12 months at any site althought trends of increase were apparent. After 20 months, further significant increases in Hg content were observed in both the terricolous lichen and the feather moss at both the Roundtop Mountain base and summit sites. A significant increase in Hg content of P. schreberi was also noted at the Mt. Tremblant summit site. Over the length of the study the greatest mercury concentration increases were observed in the feather moss at the Roundtop Mountain summit site (with a 248.3 ± 30.0 ppb mercury concentration as compared to 108.3 ± 30.0 ppb in controls). No significant change in mercury concentration in the epiphyte H. physodes was found during the study. These data indicate that mercury deposition is occurring, especially to higher elevation sites. While mercury inputs at the summits may be increased by the effects of fog, increases in mercury at the base sites cannot be accounted for the same way, but may represent the importance of dry deposition processes.     

Human exposure to mercury due to goldmining in the Tapajos River basin,Amazon, Brazil: Speciation of mercury in human hair,blood and urine

To obtain the basic information on human exposure to mercury (Hg) due to gold mining activities in Amazon, total mercury (T-Hg) and methylmercury (MeI Ig) were determined for human hair, blood and/or urine samples collected from populations living in gold mining area and fishing villages upstream of the Tapajos River basin. Abnormally high levels of T-Hg were observed in hair and blood from all fishing villages investigated and more than 90% of T-Hg was in the form of MeHg in both samples, whereas in goldrnining area the value were much lower and the %MeHg values varied widely (20–100%) with individuals even in blood samples. Urine from gold shop workers contained Hg mostly in inorganic form at 165μg/g creatinine on the average, with the range of 20 to 450μg/g creatinine. A good correlation between Hg in hair and blood was found in fishing villages and the ratios of hair Hg to blood Hg were very close to 250, generally established for MeHg. T-Hg and inorganic Hg levels in urine from gold shop workers were also significantly correlated with inorganic Hg in blood.     

Mercury in Biomass Feedstock and Combustion Residuals

An exploratory survey of the mercury content of some common California biomass feedstocks shows that the concentrations are well below EPA toxicity levels with representative feedstock concentrations of 20 ppb for rice straw, 28 ppb for wheat straw, and 32 ppb for whole-tree wood chips. The temporal variability for rice straw (17–20 ppb) is near the analytical uncertainty (～2 ppb). Saline-irrigated feedstock does not contain greatly higher mercury contents (17–38 ppb) compared to normally irrigated feedstock. Water leaching has likewise no detectable effects on mercury mobility, despite an up to 30% increase in the Hg concentrations attributable to mass losses during leaching. Combustion at temperatures of at least 575°C results in complete volatilization of mercury leaving solid ash and slag residuals with mercury contents at or near the lower limit of detection (5 ppb). The mercury strongly concentrated in fly ash can reach concentrations up to 40 times (<1,166 ppb) the corresponding fuel concentrations.     

Contaminant Transport Through Initially Dry Soil

We combined dose-response analyses with a probabilistic exposure assessment to estimate the risks to native Canadians who ingest methylmercury via fish consumption from natural lakes and a reservoir in British Columbia. Available dose-response data included multivariate measurements of central nervous system functioning in Iraqi children exposed to methylmercury prenatally. We applied the method of principal components to simplify the data structure. The first principal component described close to 80% of the variability in the data, making it a reasonable choice as an index. The relationship between mercury in maternal hair and the probability of an abnormal neurological effects index was modeled with the logistic and Weibull functions. The goodness-of-fit of the two models is discussed and the results compared to other published dose-response analyses. Exposure distributions were developed to represent methylmercury dose by using observed data on methylmercury contamination in the lakes and reservoir and reasonable assumptions about other key parameters such as fish consumption. We estimated risks to the target population using Monte Carlo simulation. Consumption of reasonable quantities of fish from these bodies of water does not pose a significant risk to the aboriginal population.     

Human exposure to mercury may decrease as acidic deposition increases

It has been hypothesized that human mercury (Hg) exposure via fish consumption will increase with increasing acidic deposition. Specifically, acidic deposition leads to reduced lake pH and alkalinity, and increased sulphate ion concentration ([SO₄ ^2?]), which in turn should cause increased Hg levels in fish, ultimately resulting in increased human Hg exposure via fish consumption. Our empirical test of this hypothesis found it to be false. We specifically examined Hg levels in the hair of Ontario Amerindians, who are known consumers of fish from lakes across the province, and observed a weak negative association with increasing sulphate deposition. An examination of Hg levels in lake trout, northern pike and walleye, three freshwater fish species commonly consumed by Ontario Amerindians, found a similar weak negative association with increasing sulphate deposition. Further analysis of these fish data found that fish [Hg] was most significantly (positively) associated with lake water concentrations of dissolved organic carbon (DOC), not pH, alkalinity or [SO₄ ^2?]. Lake DOC levels are lower in regions of greater acidic deposition. We propose an alternate hypothesis whereby human Hg exposure declines with increasing acidic deposition. In particular, we propose that increasing sulphate deposition leads to reduced lake DOC levels, which in turn leads to lower Hg in fish, ultimately reducing human Hg exposure via fish consumption.     

南方6省稻米总汞含量调查及其膳食暴露评估

为评价中国南方6省稻米中总汞污染现状,于2009年在江西、湖北、湖南、广东、广西和四川6省抽样检测了1 321份稻米样品,结合中国居民20个性别年龄组人群的稻米消费量和体重信息,采用非参数概率方法对稻米中总汞的膳食暴露量进行了评估。总汞含量采用电感耦合等离子体质谱仪（ICP-MS）测定,检出限（LOD）为0.000 8 mg.kg-1。结果表明,稻米的总汞含量在地区间存在着差异,虽然有76.2%的样本总汞含量（0.000 8～0.063 4 mg.kg-1）高于检出限,但仅有2.3%的样本超出了最高限量（ML 0.02mg.kg-1）。将评估结果比照JECFA推荐的总汞暂定每周耐受摄入量（PTWI）5μg.（kg bw）-1,我国居民食用这6省稻米产生的汞暴露风险较小。但在P99.9的高百分位水平下,14岁以下人群的摄入量相对较高,占PTWI的41.5%～62.9%,其中2～4岁儿童和4～7岁男童的摄入量占PTWI的60%以上,潜在风险较大。建议应对稻米中重金属汞的含量进行追踪监测。     

Mercury contamination in hair of riverine populations of Apiacás Reserve in the Brazilian Amazon

Total and inorganic Hg in 55 samples of hair from riverines, mainly descended from Munduruku and Apiaká Indians, living along the rivers Teles Pires and Juruena have been determined. The sampled population represents 18% of the inhabitants of the region and they eat fish 6 or 7 days a week. Cold-vapor AAS and alkaline digestion with CdCl2/SnCl2 as reducing agent were employed to estimate total Hg in hair samples. A LDC Analytical, Mod. 1255, Mercury monitor was used for Hg determination. The mean value of total Hg was 34.2µg g-1, with an average of 87.2% of organic Hg Ninety-three per cent of the sampled population present levels of Hg above 10µg g-1, and 18% over 50µg g-1. A relationship between the mean value of Hg and age of the sampled population is presented. All women at child-bearing age present concentrations of Hg above 10µg g-1. Fifty-four per cent of them had levels over 30µg g-1, with a mean of 41.2µg g-1. For the children under ten years of age, 14% show Hg concentration above 50µg g-1. Comparison of these results with those obtained in 10 other Amazon surveys (n=1672) is shown. The results of the concentration of mercury in fish, mainly piscivorous (n=967) from Amazonian and Wetland (pantanal matogrossense) are also presented, with a mean of 726 ng mg-1. There appears to be a relationship between level of Hg in human and their food ingestion habits.     

Estimating Exposure to Methylmercury: Effects of Uncertainties

Uncertainties in exposures can lead to biased estimates of slopes and thresholds in the exposure-response relationships that are developed from regression analysis. This paper reviews published exposure and epidemiological studies of methylmercury (MeHg) from the perspective of the accuracy and precision of the estimates used to represent the actual doses received. Sources of such uncertainties, collectively referred to as “exposure errors”, include instrumental and analytical errors, sampling and survey uncertainties, and individual variability in the relationships between the exposure metrics and the actual doses to target organs. Because the relationship between maternal intake and the consequent dose to the fetal brain varies among individuals, epidemiological studies of the effects of prenatal exposure must necessarily be accompanied by larger exposure uncertainties than comparable studies of effects on the mothers. The increased exposure errors typically result in attenuated slopes of the dose-response functions and under-estimates of thresholds, so that part of the apparent increased sensitivity of the fetus that has been developed from epidemiological studies may in fact be due to their inherently less certain exposures. Sources and magnitudes of exposure error found in the literature are discussed and their statistical ramifications are explored with Monte Carlo simulations. The paper also finds that, after adjusting for exposure error, the relationship between dietary intake and blood concentration is consistent with an average half-life shorter than has typically been used and that using population averages yields a consistent but sub-linear relationship between dietary intake of Hg and hair concentration. Investigators are urged to obtain (and present) data on more than one exposure metric, so that their relative uncertainties may be assessed independently.     

Methylmercury in hair samples from different riverine groups,Amazon, Brazil

The present study was aimed to evaluate comparatively the levels of methylmercury (MeHg) in human hair, collected from different groups of Amazonian populations exposed to contamined fish. The study was undertaken in fishing villages and gold mining areas, mainly in the Tapajós and Madeira river basins, two of the main tributaries of Amazon river. The study population included 125 hair samples, chosen from a collection of over one thousand samples collected in different periods. Hair analyses were conducted with a new efficient extraction technique and measured with ECD-gas chromatographer. This analytical method presented good accuracy and precision when compared with standard hair samples from IAEA. A highly significant correlation was found at the interlaboratory exercise between National Institute for Minamata Disease and our laboratory at Federal University of Rio de Janeiro. The results of the present study showed, through hair analysis, a relationship between environmental contamination by mercury and methylmercury and dietary habits of the Amazon population. The highest levels of MeHg in hair samples were found in riverine population from upper Tapajós river and in riverine population from some tributaries of Madeira river, followed by population of fishing villages from Madeira river. Majority of the women of child-bearing age presented high MeHg concentration in hair samples (10 mg.kg-1). On the other hand, Yanomami Indians presented MeHg concentration below the limit tolerable of 6 mg.kg-1.     

Mycoflora and multimycotoxin detection in corn silage: experimental study

Agricultural activities involve the use of crop preservation such as "trench-type" silo, which can sometimes be contaminated by fungi. To investigate the exposure of livestock and farm workers to fungal spores and mycotoxins, a multimycotoxin analysis method has been developed. Six mycotoxins (aflatoxin B1, citrinin, deoxynivalenol, gliotoxin, ochratoxin A, and zearalenone) were quantified by high-performance liquid chromatography coupled to mass spectrometry after solid-phase extraction. An experimental study of fungal species and mycotoxins was conducted in corn silage (Normandy, France) during 9 months of monitoring. The results indicated the recurrence of around 20 different species, with some of them being potentially toxigenic fungi such as Aspergillus fumigatus, Aspergillus parasiticus, Fusarium verticillioides, and Monascus ruber, and the detection of aflatoxin B1 (4-34 ppb), citrinin (4-25 ppb), zearalenone (23-41 ppb), and deoxynivalenol (100-213 ppb). This suggested a possible chronic exposure to low levels of mycotoxins.     

Risk Assessment of Mercury in Alta Floresta. Amazon Basin - Brazil

In the last 15 years gold mining activity has been the main source of the mercury (Hg) emissions into the atmosphere in the Amazon Basin. The first phase of gold production takes place in remote areas. In general the second one happens in the local urban area, where the gold is commercialized and sent to the great economic centers. In the last 3 years, this activity started to decline as a consequence of the high cost of the gold production but in the Municipality of Alta Floresta, the gold trade still plays an important role in the local economy. This paper addresses the assessment of the Hg exposure scenarios and their quantitative risk for inhalation of metallic Hg vapor and for ingestion of total Hg, using indirect exposure measurements, for different age groups of the urban area of Alta Floresta. This work took into account the field study which provided background information, such as characteristics of local and regional environment, Hg concentrations in different environmental media, and the character of the local urban population. The mean levels of Hg in the atmosphere of the urban area ranged from 210 ng/m³ to 880 ng/m³. Alta Floresta has no riverside population and there is a low fish consumption rate of 8 g/d among the general population. However, mercury levels in locally consumed carnivorous fish, ranged from 0.3 to 3.6 mg/kg, depending on the species and on the period of the year. The levels of mercury in soil surrounding the residential areas near the Hg emissions sources, ranged from 0.05 to 4.10 mg/kg. Hg in soil may represent an important source of mercury ingestion for local children up to 4 years of age. The mean Hazard Index estimated for the general adult population was 1.4. For the general population, regarding the number of persons exposed in the urban area, inhalation of metallic Hg vapor is the main route of exposure. The results for water ingestion for all groups are negligible. For families of fishermen the Hazard Index was estimated to be 9.3, with a contribution of 92% from fish ingestion.     

Mercury Values in Urine from Inhabitants of St. Petersburg

The results of 3000 urine analyses are presented. The observational data were obtained for the reference group of school children and adults and for groups of people suffered from indoor mercury pollution. A novel Zeeman atomic absorption spectrometer and cold vapour and piroliz methods were used for determination of total mercury. A background mercury value in urine for St. Petersburg region is determined as 0.5 μg/l. Distributions of mercury concentrations in urine after five accidents are given. There are considerable differences in total mercury distribution for each group, that depend on level of Hg exposure. Peculiar features of the 24-hour rhythm of mercury excretion with urine is used for the treatment of patients, an optimal therapy selection and rehabilitation control.     

Parallel deficits in linear growth and mental development in low-income Mexican infants in the second year of life

OBJECTIVE: To explore anthropometric indicators and mental development in very-low-income children in the second year of life. DESIGN: Cross-sectional survey. SETTING: Low-income areas (income <20th percentile) in semi-urban Mexico (defined as towns or cities with 2,500-50,000 inhabitants). SUBJECTS: Eight hundred and ninety-six children aged 12.5-23.5 months surveyed from September to December 2001. METHODS: Questionnaire survey and anthropometric survey of households. Multivariate regression models evaluated differences across age in anthropometry (height-for-age Z-score (HAZ) and weight-for-height Z-score) and cognitive function (Mental Development Index (MDI) of the Bayley Scales of Infant Development) while controlling for socio-economic and parental characteristics. RESULTS: There was a significant decline in HAZ and in age-adjusted MDI score across the second year of life. Although the children showed MDI scores close to the mean, normed US values at 13-14 months, the scores were significantly lower than expected in older children (P < 0.0001), even after controlling for socio-economic status and parental characteristics. At 13-14 months, only 3% of children received scores below 70 (less than minus two standard deviations), whereas by 19-20 months, almost 17% of children were performing below this level. No socio-economic or parental characteristics were significant predictors of HAZ or MDI. CONCLUSIONS: Parallel deficits are evident in both height-for-age and cognitive functioning during the second year of life in low-income Mexican infants. The consistency of these growth and development findings further stresses the need for targeted interventions to reduce the vulnerability of low-income Mexican children very early in life.     

A Risk Assessment for Methylmercury in Tuna

An analysis of the risk of a developmental delay or neurological impairment in children as a result of exposure to MeHg from tuna consumption was conducted. Data used as a basis for the analyses were obtained from surveys of tuna intake, MeHg concentrations in tuna, MeHg levels in the blood of pregnant women, individual relationships between dietary intake and blood levels, individual relationships between blood levels and hair levels, and individual relationships between hair levels and indices of behavioral and neurological performance. Causal or associational relationships, population variability, and uncertainty were modeled for the six data sets. Two predictive models were constructed using the model components. The first was designed to predict the risk of a delay in the onset of talking in a child of a mother who frequently consumes tuna (90 g-day-1). This model uses a one-dimensional Monte-Carlo simulation to assimilate the uncertainties. An average delay of 3-4 days was est imated. The second model was designed to compare the impact of several regulatory options on the risk among the population of tuna-eaters using a scale of central nervous system dysfunction expressly constructed for the assessment. A two-dimensional Monte-Carlo simulation was used to assimilate the distributional components describing population variability and uncertainty.