Organochlorine pesticide and mercury bioaccumulation in shark species from the South African coastline

Abstract

Organochlorine pesticide (OCP), selenium (Se) and mercury (Hg) contamination of South Africa’s marine waters potentially has deleterious effects on sharks, rays, and skates. These contaminants are released into the marine environment through numerous diffuse sources. Elasmobranchs are long-lived predators that occupy high trophic positions and are therefore prone to bioaccumulating these pollutants via food webs. However, there is still minimal research done on the levels of OCPs, Hg and Se in elasmobranchs around the coast of South Africa. The research hypotheses that were tested in this project were: 1) the OCP, Se and Hg levels in elasmobranch species along the South African coastline are due to factors such as sex, size, migratory habits, trophic position (intrinsic traits) and geographical location (extrinsic trait); 2) that the OCP, Hg and levels in elasmobranch tissues pose a health risk to humans who consume them; 3) there is an antagonistic relationship between Se and Hg concentrations in elasmobranch muscle tissue, thereby protecting elasmobranchs from Hg toxicity. Muscle tissue from 22 elasmobranch species were prepared for OCP and element (Se and Hg) analyses. The OCPs concentrations were analysed with a Shimadzu triple quadrupole GC-MS-TQ8050 NX following a QuECHERS extraction method. The Hg concentrations were determined using a flow injection mercury system (PerkinElmer FIMS 400) and the Se element concentrations were determined using an Agilent inductively coupled plasma mass spectrometry (ICP-MS) techniques. There was a statistically significant (p<0.05) correlations between levels of OCPs, especially DDxs and trace element Hg, and the trophic positions within the elasmobranchs from the coast of South Africa. However, Se was not significantly correlated with the trophic position of the species sampled. There were limited correlations between OCPs profiles in elasmobranchs and geographical regions, i.e., the east and south coasts. There were significant DDxs correlations with female elasmobranchs and increasing trophic position. There were similar significant correlations of Hg with trophic positions in all of the elasmobranchs analysed in the current study. Based on the human health risks assessment there were potential health risks associated with the consumption of elasmobranch contaminated with OCPs (notably p,p’-DDE) and Hg. Consumption of elasmobranch tissue contaminated with p,p’-DDE displayed unacceptable carcinogenic adverse health effects for M. mustelus (smoothhound shark), N. cepedianus (broadnose sevengill shark), and C. carcharias (white shark). All east coast elasmobranchs posed a possible long-term non-carcinogenic health risk based on the consumption of Hg-contaminated muscle tissue. Health risks posed by both DDxs, and Hg are iv of special concern in the houndsharks (M. mustelus) and dogsharks as these species are targeted for commercial harvesting purposes. The health value benefit of Se (HVBSe) was calculated to determine whether Se levels in elasmobranchs were high enough to counteract the toxic effects of Hg. With exception of N. cepedianus (broadnose sevengill shark), all elasmobranchs from the south coast had positive HVBSe values. Species from the east coast [G. cuvier (tiger shark), S. lewini (scalloped hammerhead shark), C. leucas (bull shark), and C. taurus (ragged tooth shark)], had negative HVBSe values that indicate the potential toxicity of Hg to these species and the humans that consume them. The data obtained support the first two hypotheses, with only the hypothesis that all elasmobranchs are protected due to the high Se content not being supported for four of the 22 species studied. This study makes an important contribution to providing much needed baseline information on OCPs, Hg and Se in the studied species.