| Summary: | A thesis submitted to the Faculty of Science, University of the
Witwatersrand in fulfilment of the requirements for the degree of
Doctor of Philosophy
University of the Witwatersrand,
Johannesburg, 2017 === iSimangaliso Wetland Park World Heritage site, located in northern KwaZulu-Natal, is one
of the most biodiverse conservation regions in southern Africa. It forms part of the
Maputaland-Pondoland-Albany biodiversity hotspot and encompasses four Ramsar
wetlands of international importance (Lake St Lucia, the Mkhuze wetlands, Lake Sibaya and
Kosi Bay). Large breeding populations of numerous species of birds and fish, as well as a
host of other endangered species are protected within the Wetland Park. Apart from its
ecological importance, resources from the Wetland Park are also used by nearby
communities for domestic and agricultural needs. Organochlorine pesticides (OCPs) have
been used extensively in the regions surrounding the Wetland Park for agricultural and
malaria control purposes, yet few data exist on the local environmental and social impacts
of these compounds. This study investigated the distribution and accumulation of OCPs in
surface sediments (n = 45), fish tissue (n = 51), crocodile fat (n = 15), and coral tissue (n =
9) from the Wetland Park to assess potential ecological and human health risks.
Substantial OCP concentrations were detected in all samples analysed. Total OCP
concentrations in sediment ranged between 120 and 911 ng g-1 dw, with ΣHCH (26–283 ng
g-1 dw) and ΣDDT (34–262 ng g-1 dw) the dominant contaminants. These concentrations
are among some of the highest detected globally this century, with most far exceeding
international soil quality guidelines. Total OCP concentrations in fish tissue samples from
Oreochromis mossambicus (Mozambique tilapia) and Clarias gariepinus (African sharptooth
catfish), ranged between 2953 and 8740 ng g-1 lw, with all residue concentrations
significantly higher than sediment values. Levels in the majority of fish samples exceeded
European Commission maximum residue limits and a preliminary risk assessment
indicated potential dietary risks associated with exposure to heptachlor, heptachlor
epoxide and dieldrin. Nile crocodiles are exposed to OCPs throughout their range within
iSimangaliso Wetland Park and contain some of the highest residue concentrations ever
recorded in crocodilian fat tissue. DDT and its metabolites were the dominant compounds
detected in most samples, with ΣDDT concentrations ranging between 520 and 3100 ng g-1
ww. Elevated levels of other OCPs were also detected, including lindane (67 – 410 ng g-1
ww), aldrin (150 – 620 ng g-1 ww) and heptachlor (170 – 860 ng g-1 ww). The analysis of
coral tissues revealed that OCPs also enter the marine environment, with ΣOCP
concentrations detected in coral tissues varying between 2300 and 3000 ng g-1 ww. ΣDDT
(140-460 ng g-1 ww), Σdrin (350-900 ng g-1 ww), Σchlor (390-1400 ng g-1 ww) were the
dominant residues detected.
This study represents the first detailed investigation into the distribution and accumulation
of OCPs in iSimangaliso. The concentrations detected in the various environmental
components analysed present a number of ecological and human health issues. A full
evaluation of the ecological and human health effects associated with OCP contamination
are beyond the scope of this thesis, although future assessments would aid in developing
appropriate management practices in the region. The continued use of OCPs has potentially
serious implications for wildlife conservation in the region and a need for greater
understanding of the risks associated with OCP exposure is required. The findings from this
study highlight the need for further and detailed investigations into the bioaccumulation
and ecotoxicological implications of these OCPs in the aquatic food web, in both freshwater
and marine environments. Specifically, further work examining the impact of OCPs on
crocodiles and coral reef health is proposed. A more in-depth risk assessment is also
recommended to better evaluate the impact of OCP exposure on residents in communities
surrounding the Wetland Park. === MT 2018
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