An assessment of the presence of heavy metals in the sediments of the lower Mvoti River system

Abstract

Excessive levels of heavy metals present in aquatic systems are often a result of anthropogenic activities. Sediment analysis for this type of contamination is often preferred over the dynamic water column. Due to accumulation of these elements over time, sediment analysis can provide a pollution-history for the site. Heavy metals at elevated levels are potentially toxic to aquatic life, and, because they bio-accumulate in food webs, are also potentially detrimental to human life. This study assesses the presence of heavy metals in the lower Mvoti River and Estuary. Levels of aluminium, arsenic, chromium, copper, iron, lead, magnesium, manganese, nickel, titanium, vanadium and zinc were determined using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The results show that the riverine and estuarine sites closest to industrial effluent discharge sites and informal settlements displayed the highest levels of heavy metal contamination. The results of the estuarine analysis were compared to current levels of heavy metals present in two other South African estuaries : the St. Lucia Estuary, also located on the north of KwaZulu Natal and the Swartkops Estuary in the Eastern Cape, as well as two international estuaries. Even though the lower Mvoti River and Estuary does experience some heavy metal sediment contamination, the above-mentioned comparisons illustrate the level of contamination is relatively low in comparison to other ecologically significant South African estuaries, and selected international estuaries. With respect to heavy metals, these results bode well for the Mvoti, a system historically reported to be in serious ecological degradation from other pollution sources.