Hair to blood mercury concentration ratios and a retrospective hair segmental mercury analysis in the Northwest Territories, Canada

Levels and trends of metals in human populations living in the Arctic

The 2021 Arctic Monitoring Assessment Program (AMAP)'s Human Health Assessment report presents a summary of the presence of contaminants in human populations across the circumpolar Arctic and provides an update to the previous assessment released in 2015. The primary objective of this paper is to summarise some of these findings by describing the current levels of metals across the Arctic, including key regional and temporal trends based on available national data and literature, and highlight knowledge gaps. Many Arctic populations continue to have elevated levels of these contaminants, and the highest levels of mercury (Hg) were observed in populations from Greenland, Faroe Islands, and Nunavik (Canada). Still, concentrations of several metals are declining in Arctic populations in regions where time trends data exist, although the declines are not consistent across all regions. The 2021 AMAP human health assessment report and this paper provide an extensive summary of levels of metals and trace elements in adults, pregnant women, and children across the Arctic.

Awareness and perceptions of contaminants in the Dehcho and sahtú regions of the Northwest Territories

The development and dissemination of health messaging is a critical component of reducing health disparities. Participants (n = 87) from a human biomonitoring study in six Dene communities responded to a survey about health communication regarding contaminants. The survey included questions on awareness of health messages and risk perceptions related to country foods and contaminants. The vast majority of participants reported eating country foods (99%) and heard that country foods had beneficial nutrients (90%). Seventy per cent of respondents had heard or seen messages about fish with high levels of mercury, and 60% had concerns about the safety or quality of country foods they consumed. Respondents who reported decreasing the number of fish they ate since hearing the messages about fish and mercury had lower (p = 0.04) mercury concentration in hair, compared to those who had not heard the messages. However, no differences in hair mercury were observed for respondents who reported to have changed their fishing location, chosen smaller fish or eaten less predatory fish since hearing the messages. Results indicate the need to examine reasons for self-reported behaviour changes, in addition to awareness. The conclusions of this study can inform the development of messaging and risk management decisions about contaminants within Indigenous populations.

Characterizing visual field loss from past mercury exposure in an Indigenous riverine community (Grassy Narrows First Nation, Canada): a cluster-based approach

BACKGROUND

Between 1962 and 1975, a chlor-alkali plant in Canada discharged approximately 9 metric tons of mercury (Hg) into the Wabigoon River. Over the following decades, biomarkers of Hg exposure of persons from Grassy Narrows First Nation (Asubpeeschoseewagong Anishinabek), located downriver from the discharge, reflected Hg concentrations in fish. Hg exposure is known to target the calcarine fissure, resulting in visual field (VF) loss. Most studies and clinical reports focus solely on peripheral VF loss; little is known about the impact of Hg on the central and paracentral portions. The present study sought to characterize the patterns of VF loss with respect to past and current Hg.

METHODS

A 28-year hair-Hg (HHg) database, created from a 1970-97 government biomonitoring program, served to select study participants with ≥ 4 year-based HHg measurements (n = 81). Blood-Hg was assessed for current exposure. Light sensitivity thresholds across the VF were analyzed monocularly, using a Humphrey Field Analyzer (HFA). Following post-hoc exclusions, based on HFA interpretation indices, 65 participants were retained. Both eyes were combined for analyses (n = 130 eyes). Unsupervised hierarchical clustering of HFA plot data was used to identify patterns of VF loss. A series of mixed effects models (MEM) were performed to test the associations for current Hg exposure with respect to HFA interpretation indices and clusters, as well as for longitudinal past Hg exposure.

RESULTS

The clustering approach decomposed the light sensitivity deficits into 5 concentric clusters, with greatest loss in the peripheral clusters. No relation was observed between any of the cluster scores and current blood-Hg. VF deficits increased with past Hg exposure. Longitudinal MEM showed that HHg was significantly (p < 0.05) associated with all peripheral, paracentral, and central cluster scores, as well as with HFA interpretation indices.

CONCLUSIONS

Past Hg exposure in Grassy Narrows First Nation was associated with present day VF loss. The cluster-based location-specific approach identified patterns of VF loss associated with long-term Hg exposure, in both the peripheral and the central areas. The functional implications of this type of visual loss should be investigated.

Exposure to mercury among Spanish adolescents: Eleven years of follow-up

The toxic effects of mercury exposure on human health are a public health concern. The most important source of this exposure is the consumption of fish and marine mammals. This study aims to describe hair mercury concentrations and their evolution from birth until eleven years of age in adolescents from the INMA (Environment and Childhood) birth cohort study, and to assess the association of hair mercury concentrations at eleven years of age with sociodemographic and dietary factors. The sample comprised 338 adolescents from the sub-cohort of Valencia (in eastern Spain). Total mercury (THg) was measured in hair samples collected at 4, 9 and 11 years old and in cord blood at birth. The equivalent of hair for cord-blood THg concentrations was calculated. Fish consumption and other characteristics at 11 years old were collected through questionnaires. Multivariate linear regression models were conducted to explore the association between THg concentrations, fish consumption and covariates. The geometric mean of hair THg concentrations at 11 years of age was 0.86 μg/g (95%CI: 0.78-0.94) and 45.2% of the participants presented concentrations above the equivalent RfD proposed by the US EPA (1 μg/g). Consumption of fish such as swordfish, canned tuna and other large oily fish was associated with higher levels of hair mercury at 11 years of age. Swordfish had the highest effect with an increase of 125% in hair mercury (95%CI: 61.2-214.9%) given a 100 g/week increase in its consumption, and, taking into account the frequency of consumption, canned tuna was the main contributor to Hg exposure among our population. The hair THg concentrations at 11 years of age represented a reduction of around 69% with respect to that estimated at childbirth. Even though THg exposure shows a sustained decreasing trend, it can still be considered elevated. INMA birth cohort studies provide a longitudinal assessment of mercury exposure in a vulnerable population, its associated factors and temporal trends, and this information could be used to adjust recommendations about this issue.

The Contribution across Three Generations of Mercury Exposure to Attempted Suicide among Children and Youth in Grassy Narrows First Nation, Canada: An Intergenerational Analysis

BACKGROUND

For 60 y, the people of Asubpeeschoseewagong Anishinabek (Grassy Narrows First Nation) have endured the effects of massive mercury (Hg) contamination of their river system, central to their traditions, culture, livelihood, and diet. In the years following the Hg discharge into the English-Wabigoon River system by a chloralkali plant in the early 1970s, there was a dramatic increase in youth suicides. Several authors attributed this increase solely to social disruption caused by the disaster.

OBJECTIVE

This research examined the possible contribution of Hg exposure across three generations on attempted suicides among today's children (5-11 y old) and youth (12-17 y old), using a matrilineal intergenerational paradigm.

METHODS

Information from the 2016-2017 Grassy Narrows Community Health Assessment (GN-CHA) survey was merged with Hg biomonitoring data from government surveillance programs (1970-1997). Data from 162 children/youth (5-17 years of age), whose mothers (n=80) had provided information on themselves, their parents, and children, were retained for analyses. Direct and indirect indicators of Hg exposure included a) grandfather had worked as a fishing guide, and b) mother's measured and estimated umbilical cord blood and childhood hair Hg and her fish consumption during pregnancy with this child. Structural equation modeling (SEM) was used to examine significant links from grandparents (G0) to mothers' exposure and mental health (G1) and children/youth (G2) risk for attempted suicide.

RESULTS

Mothers' (G1) median age was 33 y, 86.3% of grandmothers (G0) had lived in Grassy Narrows territory during their pregnancy, and 52.5% of grandfathers (G0) had worked as fishing guides. Sixty percent of children (G2) were <12 years of age. Mothers reported that among teenagers (G2: 12-17 years of age), 41.2% of girls and 10.7% of boys had ever attempted suicide. The SEM suggested two pathways that significantly linked grandparents (G0) to children's (G2) attempted suicides: a) through mothers' (G1) prenatal and childhood Hg exposure and psychological distress, and b) through maternal fish consumption during pregnancy (G1/G2), which is an important contributor to children's emotional state and behavior.

DISCUSSION

Despite minimal individual information on G0 and G1 past life experiences, the findings support the hypothesis that Hg exposure over three generations contributes to the mental health of today's children and youth. The prevalence of Grassy Narrows youth ever having attempted suicide is three times that of other First Nations in Canada. https://doi.org/10.1289/EHP11301.

Characterizing variability in total mercury hair:blood ratio in the general Canadian population

BACKGROUND/OBJECTIVES

The body burden of mercury in humans can be measured through hair or blood biomarkers. To compare results from different studies, it is often required to convert mercury in hair to an equivalent level in blood, using a default hair:blood ratio of 250:1 by the World Health Organization (WHO). However, the actual ratio may vary within and between populations. The objectives of this study were to analyze the hair:blood mercury ratio in the general Canadian population, explore factors associated with higher/lower ratios, and determine if the standard ratio of 250:1 is supported.

METHODS

The Canadian Health Measures Survey (CHMS) Cycle 5 (2016-2017) measured total mercury (THg) in both hair and blood of 1168 participants 20-59 years of age. We calculated geometric mean (GM) concentrations of THg for this entire sample and subgroups. The subgroups included biological sex, women of childbearing age, race, hair treatments, categories of blood and hair selenium, urinary arsenobetaine/arsenocholine, categories of blood and hair mercury, and food consumption. We calculated a hair:blood ratio for each participant and determined population-level ratios from the GMs of the distributions. Differences by subgroups, and agreement with the WHO ratio of 250:1, were tested. The combined effect of factors on the THg hair:blood ratio was explored using staged regression analysis.

RESULTS

For participants with paired hair and blood mercury measurements, the GM of the hair:blood THg ratio was 293 (95%CI:273-316), and significantly >250. In women of childbearing age, the ratio did not differ from 250. The GMs of the ratio were higher (i.e.>300) for second tertile blood selenium (365, 95%CI:307-433), third and fourth quartiles hair mercury (347, 95%CI:308-390 and 376, 95%CI:336-422), and consumers of shellfish (338, 95%CI:308-371). Shellfish consumption was the only statistically significant factor associated with the hair:blood ratio as identified in the regression model.

CONCLUSIONS

The mean hair:blood THg ratio among Canadians generally exceeded the default ratio of 250:1. Higher ratios were observed in certain subgroups, such as seafood consumers, and shellfish consumption was the most important variable associated with the ratio. Our results suggest that population-specific hair:blood THg ratios be considered, if possible, when converting mercury levels from hair to blood to better characterize the variation around the conversion.

Association of urinary or blood heavy metals and mortality from all causes, cardiovascular disease, and cancer in the general population: a systematic review and meta-analysis of cohort studies

Amounting epidemiological evidence has shown detrimental effects of heavy metals on a wide range of diseases. However, the effect of heavy metal exposure on mortality in the general population remains unclear. The primary objective of this study was to clarify the associations between heavy metals and mortality from all causes, cardiovascular disease (CVD), and cancer based on prospective studies. We comprehensively searched Pubmed, Embase, and Web of Science electronic databases to identify studies published from their inception until 1 March 2022. Investigators identified inclusion criteria, extracted study characteristics, and assessed the methodological quality of included studies according to standardized guidelines. Meta-analysis was conducted if the effect estimates of the same outcome were reported in at least three studies. Finally, 42 original studies were identified. The results of meta-analysis showed that cadmium and lead exposure was significantly associated with mortality from all causes, CVD, and cancer in the general population. Moderate evidence suggested there was a link between arsenic exposure and mortality. The adverse effects of mercury and other heavy metals on mortality were inconclusive. Epidemiological evidence for the joint effect of heavy metal exposure on mortality was still indeterminate. In summary, our study provided compelling evidence that exposure to cadmium, lead, and arsenic were associated with mortality from all causes, CVD, and cancer, while the evidence on other heavy metals, for example mercury, was insignificant or indeterminate. Nevertheless, further prospective studies are warranted to explore the joint effects of multiple metal exposure on mortality.

Methylmercury Risk Assessment Based on European Human Biomonitoring Data

A risk assessment (RA) was conducted to estimate the risk associated with methylmercury (MeHg) exposure of vulnerable European populations, using Human Biomonitoring (HBM) data. This RA was performed integrating published data from European HBM surveys and earlier EFSA approaches (EFSA 2012). Children/adolescents (3 to 17 years old) and women of childbearing age (18 to 50 years old) were selected as relevant study population groups for this RA. Two types of HBM datasets were selected: HBM studies (n = 18) with mercury (Hg) levels (blood and hair, total Hg and/or MeHg) in the general population in different EU countries and the DEMOCOPHES harmonized study in child–mother pairs (hair, total Hg) in 17 EU countries as a reference. Two approaches were included in the RA strategy: the first one was based on estimations of the fraction of children/adolescents and women of childbearing age, respectively, from the EU general population exceeding the HBM-I value established by the German Human Biomonitoring Commission, measured as Hazard Quotients (HQ); and the second approach was based on estimations of the fraction of the two population groups exceeding the Tolerable Weekly Intake (TWI) (or their equivalent to Tolerable Daily Intake (TDI)) defined by EFSA in 2012. The HQ approach showed that for both groups, the risk varies across EU countries and that some EU areas are close to or exceeding the exposure guidance values. This is the case of Spain and Portugal, which showed the highest HQ (GM and/or P95), probably due to their higher fish consumption. Results from the EFSA approach show that hair values of children/adolescents and women of childbearing age (both in selected HBM studies and in DEMOCOPHES study) are below the TDI of 1.9 µg/g; therefore, in general, the European population does not exceed the daily average/intake dose for MeHg and/or Hg. A possible risk underestimation was identified in our assessment since for many studies no data on P95 were available, causing loss of relevant information for risk characterization on the upper bound. In addition, data from other European countries also with high seafood consumption, such as France, Greece or Iceland, were not available. For this reason, further RA refinement is needed with harmonized and more widespread HBM data to account for differences in European exposure and associated risks, so that interventions to protect vulnerable citizens, can be applied.