Metal and metalloid bioaccumulation in the Cape white seabream (Diplodus capensis) and the tropical halfbeak (Hyporhamphus affinis)

Abstract

Metal and metalloid (collectively referred to as elements) concentrations in fish muscle and liver (tissues) along the South African coastline result from complex interactions of anthropogenic sources and natural processes. Anthropogenic sources, originating from human activities, introduce elements into the marine environment. Industrial discharges are known to contain Cd, Hg, and Pb, posing health risks to marine ecosystems and regular human consumers. Conversely, natural processes such as geological weathering and erosion can release elements in the marine environment leading to increased concentrations in fish tissue. Understanding anthropogenic sources and natural processes is vital for maintaining a healthy marine ecosystem and ensuring safe consumption of marine fish meat. The present study aimed to investigate the element concentrations in tissues of Hyporhamphus affinis (tropical halfbeak) from Sodwana Bay during two surveys and assess the associated human health risks from consuming contaminated H. affinis. The hypothesis was that there would be differences in element concentrations in tropical halfbeaks between the pre-COVID (2018) and post-COVID (2022) periods at Sodwana Bay. This was tested by comparing element concentrations in H. affinis muscle and liver tissues collected in 2018 and 2022 and evaluating the potential non-carcinogenic and carcinogenic health risks. Similarly, element concentrations in tissues of Diplodus capensis (Cape white seabream) from both minimally impacted and anthropogenically impacted sites along the South African coastline were investigated from 2020 until 2022. The aim was to assess the human health risks related to the bioaccumulation of elements in D. capensis. The assumption was that element accumulation in the Cape white seabream would reflect land-use activities, leading to higher health risks for consumers in contaminated areas. This assumption was tested by collecting specimens from different sites, analysing element concentrations in D. capensis tissues, determining element bioavailability in the marine ecosystem, as well as calculating non-carcinogenic and carcinogenic health risks associated with consuming contaminated D. capensis. The results indicated that recreational activities decreased at the beginning of the COVID19 pandemic in early 2020 at Sodwana Bay and continued to be impacted by lockdown restrictions until the end of 2021, in contrast to the higher levels of activity seen before the pandemic. Analysis of element concentrations in the tissues of H. affinis revealed distinct trends. Notably, there was a significant decrease in the levels of elements such as As, Cd, Cu, Fe, Hg, and Ni in tissues. Conversely, there was a notable increase in the concentrations of Cr, Mn, Pb, Sb and Sn in tissues. The present study observed that along the South African coastline, Chintsa had significantly higher element concentrations in muscle tissues compared to most other sites, while other sites showed relatively similar element concentrations in D. capensis. Among the different time intervals, Tsitsikamma (2021) and Chintsa (2022) had the highest element concentrations in muscle tissue. Elements in liver tissue consistently showed significant increases in most elements at Chintsa (2022) and Witsand (2021), except for Pb, which had a higher concentration in Mossel Bay. Furthermore, De Hoop (2021) and Witsand (2021) had significantly higher levels of Sn compared to the other study sites along the coast. Again, fish from Tsitsikamma (2021) and Chintsa (2022) presented the highest concentration levels within liver tissue when comparing different time intervals. The analysed elements had the potential to present carcinogenic or non-carcinogenic risks to regular human consumers. Specifically, in H. affinis muscle tissue, non-carcinogenic risks were associated with As and Hg, while carcinogenic risks were linked to As, Cr, Ni and Pb. It is important to highlight that only the concentrations of As and Hg exceeded the acceptable thresholds for non-carcinogenic risks in D. capensis across all sites along the South African coastline. The assessment of the carcinogenic risks associated with these elements in D. capensis from the surveyed locations along the South African coastline revealed that As presented a risk to people consuming D. capensis at all sites examined. The present study concluded that variations in element concentrations between the pre COVID and post-COVID periods in H. affinis were primarily due to reduced human activities in Sodwana Bay. Natural processes, such as regular upwelling events and winddriven erosion, also contributed to the observed element concentrations, as well as aerial Hg depositions from the Mpumalanga highveld led to increased Hg levels in tissues. Furthermore, Chintsa (2022) and Witsand (2021) showed the highest element concentrations, even though there are no known pollution sources. Mossel Bay (2022) had elevated Pb levels due to increased maritime traffic. The hypothesis of higher noncarcinogenic and carcinogenic risks in impacted sites was not supported, as risks were present in relatively unimpacted sites. Element concentrations in D. capensis were influenced by regular upwelling events and dispersed sources, such as geological weathering.