Mercury in tropical and subtropical coastal environments

Abstract

Anthropogenic activities influence the biogeochemical cycles of mercury, both qualitatively and quantitatively, on a global scale from sources to sinks. Anthropogenic processes that alter the temporal and spatial patterns of sources and cycling processes are changing the impacts of mercury contamination on aquatic biota and humans. Human exposure to mercury is dominated by the consumption of fish and products from aquaculture operations. The risk to society and to ecosystems from mercury contamination is growing, and it is important to monitor these expanding risks. However, the extent and manner to which anthropogenic activities will alter mercury sources and biogeochemical cycling in tropical and sub-tropical coastal environments is poorly understood. Factors as (1) lack of reliable local/regional data; (2) rapidly changing environmental conditions; (3) governmental priorities and; (4) technical actions from supra-national institutions, are some of the obstacles to overcome in mercury cycling research and policy formulation. In the tropics and sub-tropics, research on mercury in the environment is moving from an exploratory "inventory" phase towards more process-oriented studies. Addressing biodiversity conservation and human health issues related to mercury contamination of river basins and tropical coastal environments are an integral part of paragraph 221 of the United Nations document "The Future We Want" issued in Rio de Janeiro in June 2012.

Figure 1

More than 150 countries are in the tropical and subtropical zones, the large majority are small island states. Only a few countries have vast extensions of coastline in the tropics and sub-tropics (ex. Brazil, Australia, India, China, Mexico, USA, Chile, Peru, Angola). Seafood consumption varies widely among these nations, depending on size and capacity of fishing fleets and cultural values. Coastal pollution by mercury and other pollutants might have a role to play in this scenario at the local scale. Studies with Trichiurus lepturus (1) Shrestha et al., 1988 – Venezuela; (2) Mol et al., 2000 - Suriname; (3) Costa et al., 2009; Barbosa-Cintra et al., 2011 - NE Brazil; (4) Kehrig et al., 2004; Cardoso et al., 2009; Kehrig et al. 2009c; Kehrig et al., 2010; Kehrig et al., 2011; Carvalho et al., 2008; Di Beneditto et al. 2012; Muto et al., 2011; Bisi et al., 2012; Seixas et al., 2012a, ; Seixas et al., in press - SE Brazil; (5) Saei-Dehkordi et al., 2010 - Persian Gulf; (6) Prudente et al., 1997 - Philippines.

Figure 2

Annual mercury deposition (wet plus dry, including Hg(0); µg m^−2h yr⁻¹) over the tropical oceans simulated using GEOS-Chem. Deposition shown here is averaged over tropical latitudes (24°N to 24°S).

Figure 3

The seasonal variability in total mercury deposition (wet plus dry including Hg(0); µg m⁻² month⁻¹) across latitude simulated using GEOS-Chem.

Figure 4

Microbial loop and trophic transfer of methylmercury (MeHg) through a tropical estuarine food web. From Kehrig, 2011.

Figure 5

Total mercury (Hg_tot) and methylmercury (MeHg) in Crassostrea rhizophorae (mangrove oyster) transplanted between two estuaries of the Brazilian Northeast. Top panel: Mercury in suspended particulate matter (ng Hg_tot.L⁻¹) at experimental sites. March (end dry season), May (early rainy season) and August (late rainy season) 2000. High tide (H); Low tide (L). White bars contaminated estuary; gray bars non-contaminated estuary. Other panels: White symbols local oysters; Black symbols transplanted oysters. (a) and (c) contaminated estuary; (b) and (d) non-contaminated estuary. M. F. Costa, N. Sant’Anna Jr. and H.A. Kehrig, unpublished data.