Assessing the impact of liquid wastes discharge in the sea. A case study off Amanzimtoti, near Durban, Natal, South Africa

Abstract

Manufacture of the white pigment titanium dioxide (TiO₂) by the sulphate route essentially comprises extraction of mineral sands with sulphuric acid, precipitation of the titanium component and rejection of relatively large volumes of sulphuric acid and associated metallic salts. A quantitative survey of all components of the fauna, from invertebrates of >2 mm to nematodes and copepods (meiofauna) retained on a 38 μm mesh sieve, was carried out in the vicinity of the Tioxide outfall off Amanzimtoti, Natal, to determine the impact of such discharges. The benthic fauna was found to be rich and diverse, consisting in 1989 of as many as 248 taxa of macrofauna and 279 of meiofauna. Multivariate analysis of the community structure in relation to the Tioxide outfall indicates that discharge of acid-iron wastes is associated with both a modification of the nature of the invertebrate community, and with a reduction in population density in the immediate zone of dispersion. Despite the substantial quantities of acid discharged in the effluent, the evidence suggests that any biological impact is associated not with acid but with precipitation of one or a combination of metallic components from the neutralized dispersing effluent.