Field-based assessment of selected pharmaceuticals, pesticides and sediment metals using macrofauna and nematode communities in False Bay, South Africa

Abstract

False Bay supports high biodiversity but is increasingly subjected to anthropogenic pressures, including urbanisation and harbour activities. This study aimed to (1) quantify selected pharmaceuticals (e.g., acetaminophen, carbamazepine, diclofenac), herbicides (atrazine and metolachlor) and metals (Cu, Fe, Mn, Pb and Zn), (2) examine their spatial distribution, and (3) assess their potential effects on benthic assemblages. Sampling was conducted between 18 April and 14 June 2021 across 19 stations. Pharmaceuticals and herbicides were widely detected in seawater (LDL - 1.1 ng/L) and sediments (LDL - 54.6 ng/g), with higher concentrations in sediments, indicating their role as long-term contaminant reservoirs. Spatial patterns revealed localised enrichment near wastewater discharge zones and urbanised areas. Metal concentrations (1.6-7732 μg/g) were similarly elevated in anthropogenically influenced areas. However, risk quotient (RQ) remained <0.1 and metal concentrations were below ERL thresholds, suggesting a low potential of acute biological effects. Benthic assemblages were diverse and typical of coastal sandy environments, with no significant relationships detected between contaminant concentrations and community metrics. Nematode indices (MI and ITD) indicated good to high ecological quality. The single sampling design and family-level taxonomic resolution may have limited the detection of sub-lethal, chronic or species-specific responses. While contaminants are widespread and accumulate in sediments, their current concentrations are unlikely to cause acute ecological impacts benthos. However, chronic effects and the presence of unmonitored contaminants cannot be excluded. Long-term monitoring and higher taxonomic resolution are recommended to better understand and access cumulative ecological risks.