Application of solid phase adsorption toxin tracking technology (SPATT) for monitoring microcystins in farm dams in Levubu farming area, South Africa

Abstract

South Africa has scarce freshwater resources most of which are being affected by eutrophication and the resultant harmful algal blooms (HABs). Irrigation of edible plants with cyanobacteria-infested water poses an indirect threat to humans since cyanotoxins can be bioaccumulated in the irrigated plant tissues. The study assessed the applicability of the solid phase adsorption toxin tracking technology (SPATT) as an early warning tool for the passive sampling of microcystins (MCs) in farm dams around Levubu area and determine the physicochemical parameters that correlate to toxin loads in the farm dams.Three farm dams were selected and sampled monthly from June to November 2021. Physicochemical parameters monitored included electrical conductivity (EC), pH, Temperature, total dissolved solids (TDS), turbidity, chlorophyll-a and total dissolved nitrates and phosphates.Findings showed that the water temperature, pH, EC and TDS were all within optimal range for the growth of cyanobacteria. Nutrients (phosphates and nitrates) were below the detection limit. Chlorophyll-a ranged from 0.355 to 14.07 μg L−1, indicating oligotrophic to mesotrophic eutrophic status of the rivers. Among cyanoHABs identified were the Microcystis and Lyngbya genus.Both grab and SPATT samplers detected MCs in all the farm dams throughout the sampling period but there was no correlation between the MCs detected by the two methods. None of the physicochemical parameters correlated with phytoplankton biomass nor with MC levels in the water. The use of SPATT increased the likelihood of detecting MCs thus indicating the applicability of SPATT as a useful early warning tool for the presence of MCs to the water users.