THE SCIENCE AND HEALTH EFFECTS OF MERCURY: A REVIEW OF RISK AND UNCERTAINTY

Bruce Lourie

1216 Yonge Street, Suite 201

Toronto, ON M4T 1W1

blourie@lourielove.com

ABSTRACT

This paper provides an overview of the health effects of mercury (primarily methylmercury) exposure, drawing upon recent scientific field studies and government assessments. The paper also includes a presentation of mercury exposure guidelines that have been developed by health and environmental authorities in Ontario, Canada and internationally, in response to the health risks associated with exposure to methylmercury.

There are a number of uncertainties with respect to mercury in the environment other than those related to our understanding of the effects of mercury on human health. These uncertainties play a role in affecting the nature of the decisions made to control the use of mercury in Canada. The relative contributions of natural versus anthropogenic mercury, the transport and fate of mercury, ecosystem responses to mercury pollution and pollution controls, and the effectiveness of control technologies, are examples where scientific uncertainty influences policy decisions to control the use or release of mercury.

The format for the report follows this sequence and presents the discussion under five primary headings, Mercury in the Environment, Pathways of Exposure, Mercury Toxicity and Health Effects, Mercury Standards and Guidelines, Overcoming Uncertainty: A Research Agenda and Summary and Conclusions.

INTRODUCTION

The paper is based on a review of the literature concerning mercury in the environment and more specifically, the health risks and uncertainties associated with mercury in the environment. Implicit in this assessment is the supposition that there is a point where the evidence of health risks posed by mercury is sufficient to allow policy-makers to make decisions on the extent or nature of mercury control. The regulation of hazardous substances and activities generally occurs only when there is clear evidence that the hazard exists (M’Gonigle et al., 1994). Where the control measures being contemplated are potentially very costly to certain sectors, the expectations regarding level of certainty are heightened. These heightened standards of proof “may be creating cases in which activities are not as restricted as they should be” (M’Gonigle et al., 1994).

This study centres on contemporary understanding of mercury in the environment, the health effects of exposure to mercury, and the related risks and uncertainties. More specifically, the report identifies and explores the science and uncertainty of five components of mercury pollution. They are:

1. Sources and emissions.

2. Transport and fate.

3. Biological conversion and uptake.

4. Pathways of exposure.

5. Human health effects.

In simple terms, these can be thought of as the five steps in a journey that a molecule of mercury takes where the destination is a harmful effect on the health of humans or wildlife. A sufficient level of understanding is required of the scientific mechanisms for each step. Without this, the sequence of understanding is broken, as is the causal relationship between emissions and health effects. Yet, at each step there is uncertainty.

The purpose of this research is to raise the question; how much certainty is needed at each step before policy-makers can take action to control releases of mercury, when these actions impose a cost on industry?

METHODS

The paper draws out information through an interdisciplinary analysis of the science and health effects of mercury. A case study of mercury emissions from coal-fired utility boilers is used to illustrate this issue.

RESULTS AND DISCUSSION

There are a number of certainties and uncertainties with respect to mercury entering the environment. Decisions must be made based on what we know, with precaution in mind, given governments our history of waiting too long to find “certainty” when human and ecosystem health may be jeopardized. Sound environmental decision-making needs to consider a “weight of evidence” approach. There appears to be general agreement among scientists and policy-makers regarding the following:

· Hg is emitted by coal plants and they are one of the largest sources of Hg emissions in North America;

· the Midwest and Ohio Valley has the largest concentration of coal plants in North America;

· Hg, when emitted can travel hundreds or thousands of kilometres before being deposited;

· like other airborne pollutants it is transported with prevailing winds and in this case, travels north and north east and is deposited in Ontario, Quebec, the Maritime provinces and New England;

· mercury levels in these regions are higher than in any other part of North America, particularly in Canada’s maritime provinces;

· mercury converts to the more toxic and bioavailable methylmercury in water bodies and is consumed by aquatic organisms;

· mercury bioaccumulates and biomagnifies at a greater rate than almost any other substance we know;

· mercury can be measured increasingly dangerous levels of mercury in fish and wildlife in the northeast;

· Hg fish advisories exist for many of the lakes in these regions and the midwest;

· people continue to consume the fish and want to be able to fish without restrictions placed on them by industrial practices;

· small amounts of mercury in the organs of humans and other species can cause serious neuro-behavioral disorders;

· 60% of the population of Inuit communities have mercury levels at or above the World Health Organisation increased risk level.

REFERENCES

Davidson P.W., Myers G.J., Cox C., Axtell C., Shamlaye C., Sloane-Reeves J. et al. August 26, (1998), Effects of prenatal and postnatal methylmercury exposure from fish consumption on neurodevelopment: Outcomes at 66 months of age in the Seychelles Child Development Study. JAMA. 280(8): 701-707.

Grandjean P., Weihe P., White R.F., Debes F., Araki S., Yokoyama K., Murata, K., Sorensen, N. Dahl, R. and Jorgensen, P.J. (1999), Cognitive deficit in 7-year-old children with prenatal exposure to methylmercury. Neurotoxicology and Teratology. 20(1): 1-12. Referenced in Health Canada.

Health Canada (Medical Services Branch). (1999), Methyl Mercury in Canada: Exposure of First Nations and Inuit Residents to Methylmercury in the Canadian Environment (Volume 3). Ottawa.

US EPA-Office of Research and Development (ORD). (November 1999), Mercury Research Strategy (DRAFT).

US EPA (U.S. Environmental Protection Agency). (1997), Mercury Study: Report to Congress. Volume 1: Executive Summary. Office of Air Quality Planning and Office of Research and Development. Washington, DC.