Organochlorine Pesticides in Sediment-Dwelling Animals from Mangrove Areas of the Calabar River, SE Nigeria

  •  Orok E. Oyo-Ita    
  •  Bassey O. Ekpo    
  •  Peter A. Adie    
  •  John O. Offem    


Sediment-dwelling biota such as mollusks (clam) and crabs collected from mangrove areas of the Calabar River are important routes of exposure to organochlorine pesticides (OCPs) contamination. Residual levels of OCPs including HCHs, DDTs, heptachlor, heptachlor epoxide, aldrin, endrin ketone, entrin aldehyde, dieldrin, endosulfan, endosulfan sulphate, methoxychlor, were determined in these organisms. The results revealed the OCP loads to be predominated by DDTs and HCHs (much of which was derived from illegal usage of GAMMALIN 20 for fishing) with the overall means of 49.6 and 35.1 ng/g wet weight (ww), respectively, at 100% frequencies of occurrence. Concentrations of other OCP components were generally low and were not detected in all biota samples. This probably reflects low utilization of these OCPs in the region and/or low bioaccumulation potential in the biota species. In general, the OCP concentrations were higher in freshwater mollusks and crabs than in brackish water, indicating that freshwater biota were more easily influenced by OCPs than their brackish water counterparts. One way analysis of variance (ANOVA) indicated no significant relationship between lipid content (LC) or body size of organisms and contaminant load, probably because of the non-equilibrium situation: smaller animals accumulated more OCPs than their larger counterparts, suggesting different uptake and elimination rates for these compounds. Biota-sediment accumulation factors (BSAFs) for DDTs and HCHs varied among the organisms and were in the ranges 1.02 – 9.78 and 0.74 – 8.72, respectively, indicating probably that HCHs were less bio-available in the river than DDTs. They were generally lower for highly polluted site (UMA; freshwater area) and higher for areas of low anthropogenic pressure (MR- brackish water area). Risk assessment matched against various standards clearly showed that the biota were highly contaminated with HCHs and DDTs, and may pose serious health threats to local inhabitants of the catchments. Furthermore, other selected OCPs such as heptachlor and dieldrin may in addition pose life-time cancer risk, especially to residents of the riverine/coastal communities who often consume more of these organisms than those living inland.

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