Using Folsomia candida (Collembola) for the ecological assessment of sediment samples from three rivers from the QwaQwa region, South Africa

Abstract

AbstractSince the establishment of a free economic zone and a simultaneous increase in the population of the QwaQwa region, aquatic systems of the area were expected to undergo an increase in metal contamination. The aims of this study were to assess the quality of sediments from the Metsi-Matsho, Namahadi and Elands Rivers of the QwaQwa region, and to investigate their impact on the survival and reproduction of the collembolan Folsomia candida. Due to the lack of freshwater sediment quality guidelines in South Africa, metal contents of the sediments were analysed and critically interpreted using the national action list for the screening of dredged sediment proposed for marine disposal, and international sediment quality guidelines (SQGs). In the laboratory, F. candida was exposed to 0, 50, 75 and 100% of the sediment samples for 28 days at 20 °C. Sediments were variably contaminated with Cr, with the Namahadi River middle site having the highest concentration (569 mg.kg−1, dry weight) followed by the lower site on the Elands River (529 mg.kg−1, dry weight), both above the recommended prohibition level of 500 mg Cr.kg−1. According to the consensus-based SQGs, only the concentrations of Cr and Ni (upper reach of Metsi-Matsho River) were higher than probable effect concentration, denoting that harmful effects of those metals are likely to occur. Of the two endpoints assessed, reproduction was the most sensitive with the upper reach of the Metsi-Matsho River (half maximal effective concentration, EC50 = 24% sediment) being the most deleterious site to the reproduction of F. candida. Ecotoxicological bioassays using F. candida could be suitable complements to chemical analysis in the assessment of the ecological risks of freshwater sediments as this collembolan species is sensitive to sediments with variable ranges of metal contamination.