Metal bioaccumulation, membrane integrity and chlorophyll content in the aquatic macrophyte ceratophyllum demersum from the Diep River, Western Cape

Abstract

The Diep River is approximately 80 km in length and runs through agricultural land and urban parts of greater Cape Town, South Africa before entering the Atlantic Ocean, via an estuary. Generally, metal pollution in South African rivers is not well documented and using plants to monitor metal bioaccumulation is even less documented. The aim of this study was to investigate aluminium, iron, copper and zinc metal pollution in the Diep River and bioaccumulation of these metals in the leaves and stems of the submerged macrophyte Ceratophyllum demersum L. Furthermore, the effects of bioaccumulated metals on membrane integrity and chlorophyll content of these plants were investigated. Site 1 was situated in the upper reaches of the river adjacent to agricultural land, while site 2 was in an urban area, where industrial activities predominate. C. demersum (from an uncontaminated source) were introduced into the river at the two sites and compared with one another on a fortnightly basis over a 12 week period. Plants at site 2 were also compared to existing plants that were naturally growing at the site. Comparisons were also made between leaves and stems of the plants, to establish the organ of preference regarding metal accumulation and storage. Samples were digested with nitric acid and an ICP-MS was used to analyse metal concentrations in the water, sediment and plants. Chlorophyll extraction was done using dimethyl sulphoxide (DMSO) and the absorbance values determined using a spectrophotometer. Chlorophyll a, chlorophyll b and total chlorophyll contents were recorded and compared. Cell membrane integrity was determined by leaving plants for 24 hours in deionised water and measuring electrical conductivity and solutes (sodium, calcium, potassium and magnesium) before and after placement of the plants.