This is the second in a planned series of posts relating to mercury exposure and toxicity (see also Part 1: measuring mercury exposure and Part 3: the many faces of mercury). In this part I’m going to look at some of the causes of high mercury levels measured in the population, and specifically at a recent population biomonitoring study conducted in New York (McKelvey et al., 2011) where follow-up interviews were conducted with people who had abnormally high levels of inorganic mercury in urine samples (the mercury in urine is almost totally inorganic). The methodology was based on the methods used by the CDC for the National Health and Nutrition Examination Survey (NHANES), and included 1,840 people across a variety of social strata, ethnicities, races, and education levels.
The geometric mean measured mercury concentration was 0.73 μg/L (0.69 μg/g creatinine) and the 95th percentile was 4.35 μg/L (3.75 μg/g creatinine) – slightly higher than the national average levels I discussed previously, but not enormously high. A few trends were apparent in the data:
- Women, on average, had slightly higher mercury concentrations than men.
- Mercury levels generally increased with age until a peak at ages 40-49, after which they began to decrease.
- There was a strong correlation between the frequency of fish or shellfish consumption and mercury levels (although the trend isn’t as strong from concentrations in urine as concentrations in blood)
One additional trend emerged. A total of 13 people had mercury concentrations of 20 μg/L or higher; concentrations that high must be reported to the New York Department of Health and are normally associated with occupational exposures. However, all of these levels were measured in women, and all were visible minorities (11 Hispanic and 2 black). Ten of the Hispanic women had been born in the Dominican Republic, including 4 who had mercury concentrations exceeding 50 μg/L and one who had a mercury level of 95 μg/L (more than 100 times higher than the average person in the study). Further analysis of the population as a whole showed that Caribbean-born blacks and Dominicans had the higher average mercury concentrations than other ethnic groups considered in the study.
Most of these women were found to have been using skin-lightening creams which turned out to have illegally high levels of mercury. The authors noted that mercury applied to the skin is actually more likely to be absorbed and accumulate in the kidneys than ingested inorganic mercury, which explains the effect these creams were having on measured mercury exposure levels. While mercury concentrations in skin products are subject to stringent limits in the US, many other countries don’t have the same regulations, and several other skin products imported from other countries, and in particular the Dominican Republic, were found to have mercury levels well above the US limit, including other skin-lightening and beauty creams and antiseptic soaps and creams (some of which were labeled as manufactured in the European Economic Community). Various public health actions were taken, including seizure of products, embargoes, and press releases to the public to stop using these products.
The relationship between mercury and fish/shellfish consumption was less surprising. While the mercury from fish and shellfish is primarily organic (methylmercury) and the mercury measured in urine is primarily inorganic, it is believed that some methylmercury is converted to inorganic mercury by the body and excreted.
This particular study didn’t include a survey of the use of dental amalgams. Some studies (e.g. Akesson et al., 1991 and Kingman et al., 1998) were noted as having found the presence of amalgam fillings to be associated with mercury levels in urine, although the levels reported are much lower than those associated with some of the other exposure sources in this study; for example, German biomonitoring found people with at least amalgam fillings had mercury concentrations about twice the overall population average (which was lower than that measured in the US or in the New York study). Other studies have found traditional medicines to be a significant source of mercury exposure.
The McKelvey et al. (2011) study is an example how chemical exposures may come from unexpected sources. Other than occupational exposures, consumer products are often a major source, particularly poorly regulated products. Mercury levels associated with fish/shellfish ingestion and amalgam fillings are relatively insignificant compared to the levels associated with imported skin care products in this particular study.
As I have previously mentioned, it is important to keep in mind that an above-average mercury concentration is not necessarily associated with actual toxicity (although the extreme levels measured in some individuals in the New York study are of concern); I’ll provide more information on actual mercury toxicity in future posts in this series. It’s also important to remember that the results of provoked urine tests shouldn’t be compared to the levels I’ve been discussing here (or to anything else – as I discussed previously, provoked urine testing is essentially a scam to trick people into thinking they have high mercury levels so they pay for expensive and generally unnecessary treatments).
Akesson I, Schutz A, Attewell R, Skerfving S, & Glantz PO (1991). Status of mercury and selenium in dental personnel: impact of amalgam work and own fillings. Archives of environmental health, 46 (2), 102-9 PMID: 2006894
Kingman, A., Albertini, T., & Brown, L. (1998). Mercury Concentrations in Urine and Whole Blood Associated with Amalgam Exposure in a US Military Population Journal of Dental Research, 77 (3), 461-471 DOI: 10.1177/00220345980770030501
McKelvey, W., Jeffery, N., Clark, N., Kass, D., & Parsons, P. (2010). Population-Based Inorganic Mercury Biomonitoring and the Identification of Skin Care Products as a Source of Exposure in New York City Environmental Health Perspectives, 119 (2), 203-209 DOI: 10.1289/ehp.1002396