Acute toxicity of preservative chemicals in organic baits used in carp, Cyprinus carpio , recreational fishing

Boilies are specialised baits used in carp, Cyprinus carpio L., recreational fishing. They are made from different meals (e.g. fish meal, soya bean meal), eggs, flavours, feeding stimulants and are boiled in water for hardening (Niesar, Arlinghaus, Rennert & Mehner 2004; Arlinghaus & Niesar 2005). As a result of the popularity of specialised carp fishing throughout Europe, boilies are introduced into water bodies in large amounts, potentially contributing to eutrophication (Arlinghaus & Mehner 2003; Niesar et al. 2004). In addition to nutrients such as phosphorus, some boilie types, particularly those produced commercially, contain preservative chemicals (PC) to prevent deterioration and fungal infestation. The two main preservative chemicals (PCs) used in many ready-made boilies are benzoic acid (BA) and potassium sorbate (PS), or a combination thereof (Anonymous, personal communication 2005). Several studies describe the toxicity of BA to aquatic organisms ranging from bacteria to fish (e.g. Zhao, Ji, Cronin & Dearden 1998; Saha, Bhunia & Kaviraj 2006). Potassium sorbate is the salt of sorbic acid, which is also toxic to multiple aquatic organisms including fish, but lethal concentrations of sorbic acid for fishes are up to 6.5 times higher than those of BA (Koch 1994; Roth 1999). No studies describe the toxicological risk of BA and PS used as preservatives in angling baits. The objective of the present studywas to assess the acute toxic effects of boilies containingBAand PS bymeasuring the lethal concentrations where 50%of embryos of the model organism zebrafish, Danio rerio (L.), died within 48 h (48-h, LC50). Adult zebrafish were kept in an 80-L glass aquarium at 26 C with a day–night rhythm of 12:12 h. A metal grate was installed at the bottom of the aquarium, through which fertilised eggs could pass, thereby reducing potential egg predation by adults. Below this grate, a funnel led into a tube through which the eggs were collected. After sampling, the eggs were cleaned with reconstituted water at 26 C. Reconstituted water contained 294.0 mg L CaCl2, 123.3 mg L )1 MgSO4, 63.0 mg L NaHCO3 and 5.5 mg L )1 KCl. Two series of toxicological tests, range-finding-tests with pure substances and tests with boilies containing BA (Merck Darmstadt, Germany) and PS (Fluka Chemie Neu Ulm, Germany), were conducted according to a German standard using the fish egg model zebrafish described in detail in DIN-Norm 38415-T6 (2001). The range-finding-tests were done because the reported toxicity range of BA to zebrafish eggs was very wide (DIN-Norm 38415-T6 2001) and data about