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

Hematological Parameters and Mercury Exposure in Children Living Along Gold-Mining-Impacted Rivers in the Mojana Region, Colombia

Mercury (Hg) exposure is a key determinant of human health, arising from environmental, occupational, and domestic sources, as well as the consumption of contaminated food, particularly fish. Due to their developmental stage and heightened susceptibility, children are especially vulnerable. This study evaluated Hg contamination in a high-risk pediatric population affected by local economic activities such as small-scale gold mining, agriculture, and fishing. The objective was to determine whether exposure to this toxic metal was associated with alterations in hematological biomarkers, analyzing potential correlations with total Hg (T-Hg) levels in the hair and blood of 282 children aged 6 to 12 years in the Mojana Bolivarense (Colombia). The mean T-Hg concentration in hair was 0.88 µg/g in Magangue, 1.55 µg/g in Achi, and 0.26 µg/g in Arjona. A total of 35.0% and 44.4% of the examined minors from Magangue and Achi, respectively, exceeded the international threshold for hair Hg (1 µg/g). Likewise, blood T-Hg concentrations surpassed the recommended safety level (5 μg/L) in 39.4% of children from Achi and 0.8% from Magangue, while in Arjona, all values remained below this threshold. The geometric mean (GM) values of the hair-to-blood Hg ratio varied across locations. Spearman correlations revealed a very strong positive association between blood and hair T-Hg levels in Achi (ρ = 0.801; p < 0.01), a moderate correlation in Magangue (ρ = 0.325; p < 0.01), and some significant links with hematological parameters. Multiple linear regression analysis indicated a positive association between blood T-Hg concentration and white blood cell count (β = 0.053; p = 0.021) and granulocytes (β = 0.086; p = 0.011), as well as an inverse correlation with lymphocyte percentage (β =  - 0.353; p = 0.036). These findings suggest that Hg exposure may influence inflammatory and immunosuppressive processes, posing a potential health risk to vulnerable populations, particularly young individuals.

Review of non-invasive biomarkers as a tool for exposure characterization in human health risk assessments

Blood and urine are historically the most frequent matrices used for measuring chemical levels in human biomonitoring studies. As biomonitoring programs are refreshed, consideration of specific priority substances and specific population targets provide opportunities for inclusion of alternative non- or minimally invasive matrices. This review describes methods used in health risk assessment to characterize exposure and risk based upon biomarkers from noninvasive matrices other than urine or blood, including human milk, hair, fingernails, toenails, exhaled breath, deciduous teeth, sweat, semen, meconium, and feces. Illustrative examples of these methods relevant to chemical management are provided. This review suggests that, although these alternative noninvasive biomarkers are not frequently used in human health risk assessment at present, these biomarkers may prove useful in (1) characterizing exposure and health risk in vulnerable populations, (2) cumulative risk assessments, and (3) community-based risk assessments, depending upon the substance of concern. To incorporate alternative noninvasive biomarkers into human health risk assessments with confidence, more research is needed to improve our knowledge of the relationships between external dose, internal dose, and biologic consequent effects in matrices other than blood and urine.

Re-thinking the link between exposure to mercury and blood pressure

Hypertension or high blood pressure (BP) is a prevalent and manageable chronic condition which is a significant contributor to the total global disease burden. Environmental chemicals, including mercury (Hg), may contribute to hypertension onset and development. Hg is a global health concern, listed by the World Health Organization (WHO) as a top ten chemical of public health concern. Most people are exposed to some level of Hg, with vulnerable groups, including Indigenous peoples and small-scale gold miners, at a higher risk for exposure. We published a systematic review and meta-analysis in 2018 showing a dose-response relationship between Hg exposure and hypertension. This critical review summarizes the biological effects of Hg (both organic and inorganic form) on the underlying mechanisms that may facilitate the onset and development of hypertension and related health outcomes and updates the association between Hg exposure (total Hg concentrations in hair) and BP outcomes. We also evaluated the weight of evidence using the Bradford Hill criteria. There is a strong dose-response relationship between Hg (both organic and inorganic) exposure and BP in animal studies and convincing evidence that Hg contributes to hypertension by causing structural and functional changes, vascular reactivity, vasoconstriction, atherosclerosis, dyslipidemia, and thrombosis. The underlying mechanisms are vast and include impairments in antioxidant defense mechanisms, increased ROS production, endothelial dysfunction, and alteration of the renin-angiotensin system. We found additional 16 recent epidemiological studies that have reported the relationship between Hg exposure and hypertension in the last 5 years. Strong evidence from epidemiological studies shows a positive association between Hg exposure and the risk of hypertension and elevated BP. The association is mixed at lower exposure levels but suggests that Hg can affect BP even at low doses when co-exposed with other metals. Further research is needed to develop robust conversion factors among different biomarkers and standardized measures of Hg exposure. Regulatory agencies should consider adopting a 2 µg/g hair Hg level as a cut-off for public health regulation, especially for adults older than child-bearing age.

What does scientometry tell us about mercury toxicology and its biological impairments?

Mercury is a toxic pollutant that poses risks to both human and environmental health, making it a pressing public health concern. This study aimed to summarize the knowledge on mercury toxicology and the biological impairments caused by exposure to mercury in experimental studies and/or diagnosis in humans. The research was conducted on the main collection of Web of Science, employing as a methodological tool a bibliometric analysis. The selected articles were analyzed, and extracted data such as publication year, journal, author, title, number of citations, corresponding author's country, keywords, and the knowledge mapping was performed about the type of study, chemical form of mercury, exposure period, origin of exposure, tissue/fluid of exposure measurement, mercury concentration, evaluation period (age), mercury effect, model experiments, dose, exposure pathway, and time of exposure. The selected articles were published between 1965 and 2021, with Clarkson TW being the most cited author who has also published the most articles. A total of 38% of the publications were from the USA. These studies assessed the prenatal and postnatal effects of mercury, emphasizing the impact of methylmercury on neurodevelopment, including motor and cognitive evaluations, the association between mercury and autism, and an evaluation of its protective effects against mercury toxicity. In observational studies, the blood, umbilical cord, and hair were the most frequently used for measuring mercury levels. Our data analysis reveals that mercury neurotoxicology has been extensively explored, but the association among the outcomes evaluated in experimental studies has yet to be strengthened. Providing metric evidence on what is unexplored allows for new studies that may help governmental and non-governmental organizations develop guidelines and policies.