Fishing groundbaits as an under-recognised source of nutrients and heavy metals in freshwater ecosystems

Fish baiting is an important pathway for the introduction of biogenic elements, particularly nitrogen and phosphorus, into freshwater ecosystems, and groundbaits may also contain heavy metals that intensify environmental degradation. This study assessed the extent of groundbait use in Poland and its potential ecological impacts, addressing a globally under-recognised source of anthropogenic pressure on inland waters. This study combined a survey of 1,574 anglers with chemical analyses of 12 commercially available groundbait mixtures, quantifying the nutrient content and concentrations of Hg, Cd, Pb, and As. Aquarium experiments were conducted to examine the nutrient release dynamics and associated changes in selected physicochemical water parameters. More than 60% of the respondents reported the regular use of groundbaits, predominantly ready-made commercial products. Chemical analyses revealed pronounced variability among the mixtures, with carp-oriented groundbaits exhibiting the highest concentrations of nutrients and heavy metals. All analysed baits contained detectable levels of heavy metals, raising concerns regarding food safety and human health. Experimental results demonstrated rapid nutrient release, leading to measurable changes in dissolved oxygen, pH and conductivity. Overall, groundbait use was identified as a significant yet often overlooked source of eutrophication and toxicological pressure on freshwater ecosystems, highlighting the need for responsible use guidelines and further field-based research.