Ecological and human health risk assessment of selected endocrine disrupting phenolic compounds in potable water and treated wastewater effluent in the Western Cape, South Africa

Abstract

Potable water is becoming increasingly scarce in Cape Town, Western Cape- South Africa due to climate change effects such as drought. The region’s water resources are under threat by industrial and agricultural pollution due to the release of organic contaminants such as phenol into water bodies. This reduces water quality, thereby decreasing the availability of clean water. Potable water (tap and bottled) as well as effluent from wastewater treatment plants (WWTPs) are among the most important freshwater resources in the Western Cape. This study focused on two phenolic compounds - 2,4-dichlorophenol and 4-chlorophenol. Samples of a wastewater treatment plant effluent, tap water, and four brands of bottled water were analysed for the two phenolic compounds using the HPLC/DAD. Toxicity assessment of the WWTP effluent was conducted using Raphidocelis subcapitata (a primary producer), Daphnia magna, a primary consumer that feeds on algae and Tetrahymena. thermophila a protozoan (decomposer). The Ames mutagenicity test was conducted using the T98, T100 strain and with the S9 activation enzyme. Two brands of bottled water, tap water and WWTP effluent (found to have the highest concentrations of 2,4-DCP and 4-CP) were tested for mutagenicity. The potential risk of using these water sources for potability was assessed. The phenolic compounds were both below the regulatory limits in all the samples analysed. . The concentrations of 2,4-DCP in the WWTP effluent, tap water and bottled water brands ‘A’, ‘B’, ‘C’ and ‘D’ ranged from; ND-5.40×10ˉ⁶, ND- 1.90×10ˉ⁵, ND-1.31×10ˉ⁵, 3.68×10ˉ⁶ - 1.37×10ˉ⁵, ND-6.85×10ˉ⁶ and 6.28×10ˉ⁶ - 1.47×10ˉ⁵ respectively. Corresponding values for 4-CP were 4.04×10ˉ⁶ - 5.61×10ˉ⁵, 9.96×10ˉ⁶ - 1.90×10ˉ⁵, ND-5.81×10ˉ⁶, ND-6.95×10ˉ⁶, ND-9.78×10ˉ⁶ and 8.90×10ˉ⁷ - 6.74×10ˉ⁶ (mg/L) respectively. The cumulative immobility of daphnids in a Daphina Magna test against the effluent during the test period of 48 h indicated a clear minute concentration-response relationship. Throughout the 48 h test period, there were no significant deaths of the daphnia ( i.e 1/20 to a maximum of 6/20 in all different concentrations). For the Raphidocelis subcapitata, the results showed a substantial constant increase or growth of algae throughout the 72 h period in all different concentrations (including the 100% undiluted effluent) thus indicating the eutrophic potential of the effluent. The T. thermophila toxicity test showed that the diluted effluent samples were more toxic that the whole effluent. All the samples tested exhibited strong mutagenicity on the T98 strain but slight mutagenicity on the T100 strain. All the samples were classified to have non-carcinogenic adverse effects but not cancer risk.