Northern Australia, whither the mercury?

Abstract

Biomagnification of mercury (Hg) leads to high concentrations in fish and subsequent health risks for fish-eaters. Despite the global concern afforded to Hg over the past 40 years, little attention has been paid to this toxic heavy metal in Australia in general, and tropical northern Australia in particular. This review examines past Hg research in Australia and explores seven hypotheses as to why so little research and monitoring has been conducted in northern rivers and estuaries. We rule out the possibility that fishing intensity (an indicator of potential Hg exposure in humans) is lower in Australia than in other countries with more intensive Hg research programs. Instead, we hypothesise that low atmospheric deposition, owing to prevailing wind direction and few local point sources, coupled with highly productive waterbodies, contributes to low Hg bioaccumulation and hence the reduced interest in measuring Hg. Outstanding questions regarding Hg in northern Australia include the assessment of atmospheric deposition rates of Hg, the trophic level and growth and food consumption rates of consumers such as large-bodied fishes, linkages between fire regimes and Hg availability, and the capacity for in situ Hg methylation in tropical systems.