Toxicity of emerging antifouling biocides to non-target freshwater organisms from three trophic levels

Antifouling (AF) systems provide the most cost-effective protection against biofouling. Several AF biocides have, however, caused deleterious effects in the environment. Subsequently, new compounds have emerged that claim to be more environment-friendly, but studies on their toxicity and environmental risk are necessary in order to ensure safety. This work aimed to assess the toxicity of three emerging AF biocides, tralopyril, triphenylborane pyridine (TPBP) and capsaicin, towards non-target freshwater organisms representing three trophic levels: algae (Chlamydomonas reinhardtii), crustacean (Daphnia magna) and fish (Danio rerio). From the three tested biocides, tralopyril had the strongest inhibitory effect on C. reinhardtii growth, effective quantum yield and adenosine triphosphate (ATP) content. TPBP caused sub-lethal effects at high concentrations (100 and 250μgL^-1), and capsaicin had no significant effects on algae. In the D. magna acute immobilisation test, the most toxic compound was TPBP. However, tralopyril has a short half-life and quickly degrades in water. With exposure solution renewals, tralopyril's toxicity was similar to TPBP. Capsaicin did not cause any effects on daphnids. In the zebrafish embryo toxicity test (zFET) the most toxic compound was tralopyril with a 120h - LC₅₀ of 5μgL^-1. TPBP's 120h - LC₅₀ was 447.5μgL^-1. Capsaicin did not cause mortality in zebrafish up to 1mgL^-1. Sub-lethal effects on the proteome of zebrafish embryos were analysed for tralopyril and TPBP. Both general stress-related and compound-specific protein changes were observed. Five proteins involved in energy metabolism, eye structure and cell differentiation were commonly regulated by both compounds. Tralopyril specifically induced the upregulation of 6 proteins implicated in energy metabolism, cytoskeleton, cell division and mRNA splicing whilst TPBP lead to the upregulation of 3 proteins involved in cytoskeleton, cell growth and protein folding. An ecological risk characterization was performed for a hypothetical freshwater marina. This analysis identified capsaicin as an environment-friendly compound while tralopyril and TPBP seem to pose a risk to freshwater ecosystems. Noneless, more studies on the characterization of the toxicity, behaviour and fate of these AF biocides in the environment are necessary since this information directly affects the outcome of the risk assessment.

Tralopyril bioconcentration and effects on the gill proteome of the Mediterranean mussel Mytilus galloprovincialis

Antifouling (AF) systems are used worldwide as one of the most cost-effective ways of protecting submerged structures against heavy biofouling. The emergence of environmentally friendly AF biocides requires knowledge on their environmental fate and toxicity. In this study we measured the bioconcentration of the emerging AF biocide tralopyril (TP) in the Mediterranean mussel Mytilus galloprovincialis and investigated the effects of TP on the mussel gill proteome following acute (2days) and chronic (30days) exposure, as well as after a 10-day depuration period. The experiments were carried out with 1μg/L TP; blank and solvent (5×10(-5)% DMSO) controls were also included. Proteomics analysis was performed by mass spectrometry-based multidimensional protein identification technology (MudPIT). Differentially expressed proteins were identified using a label-free approach based on spectral counts and G-test. Our results show that TP is rapidly accumulated by mussels at concentrations up to 362ng/g dw (whole tissues), reaching steady-state condition within 13days. Ten days of depuration resulted in 80% elimination of accumulated TP from the organism, suggesting that a complete elimination could be reached with longer depuration times. In total, 46 proteins were found to be regulated in the different exposure scenarios. Interestingly, not only TP but also DMSO alone significantly modulated the protein expression in mussel gills following acute and chronic exposure. Both compounds regulated proteins involved in bioenergetics, immune system, active efflux and oxidative stress, often in the opposite way. Alterations of several proteins, notably several cytoskeletal ones, were still observed after the depuration period. These may reflect either the continuing chemical effect due to incomplete elimination or an onset of recovery processes in the mussel gills. Our study shows that exposure of adult mussels to sublethal TP concentration results in the bioconcentration of this biocide in the tissues and modulates the expression of several proteins that may intervene in important metabolic pathways.