Mixture toxicity of wood preservative products in the fish embryo toxicity test

Abstract

Wood preservative products are used globally to protect wood from fungal decay and insects. We investigated the aquatic toxicity of five commercial wood preservative products, the biocidal active substances and some formulation additives contained therein, as well as six generic binary mixtures of the active substances in the fish embryo toxicity test (FET). Median lethal concentrations (LC50) of the single substances, the mixtures, and the products were estimated from concentration-response curves and corrected for concentrations measured in the test medium. The comparison of the experimentally observed mixture toxicity with the toxicity predicted by the concept of concentration addition (CA) showed less than twofold deviation for all binary mixtures of the active substances and for three of the biocidal products. A more than 60-fold underestimation of the toxicity of the fourth product by the CA prediction was detected and could be explained fully by the toxicity of one formulation additive, which had been labeled as a hazardous substance. The reason for the 4.6-fold underestimation of toxicity of the fifth product could not be explained unambiguously. Overall, the FET was found to be a suitable screening tool to verify whether the toxicity of formulated wood preservatives can reliably be predicted by CA. Applied as a quick and simple nonanimal screening test, the FET may support approaches of applying component-based mixture toxicity predictions within the environmental risk assessment of biocidal products, which is required according to European regulations.

Predicting acute and chronic effects of wood preservative products in daphnia magna and pseudokirchneriella subcapitata based on the concept of concentration addition

“…The case of product A with the dissipated active substance IPBC demonstrates the importance of analytical verifications of nominal test concentrations in order to correctly define the composition of the mixture that is assessed. In a previous study with fish embryos , IPBC concentrations were found to drop to approximately 60% of the initial concentration after 48 h of exposure, while the concentrations of propiconazole and fenoxycarb remained stable. Yet, all mixture toxicity predictions and comparisons with observed toxicity ignored changes in the mixture composition during the exposure period.…”

“…It is important to note that algal growth inhibition was still the most sensitive measured endpoint for the toxicity of product B, thereby rendering the underestimation of Daphnia acute toxicity irrelevant in the context of an environmental risk assessment. Yet, this does not prove that mixture toxicity underestimation is in general only relevant for the endpoint that is the most sensitive for the individual mixture components (algae were more sensitive than Daphnia and fish embryos for all 3 active substances investigated). Let us assume that the degree of toxicity underestimation is very large for an endpoint that is not the most sensitive for any of the individual mixture components.…”

“…Assuming a correct ecohazard labeling of the product, this appears rather unlikely. Furthermore, a previous study with product A tested in zebrafish embryos found no evidence for unidentified toxic formulation additives but instead good compliance between observed and predicted mixture toxicity based on the active substances only . As demonstrated by the toxic unit approach, even cobalt (introduced as a formulation additive) contributed little to the overall toxicity despite its known aquatic toxicity.…”

Time-dependence in mixture toxicity prediction

“…Such research has included in vitro and in vivo studies (Boyd et al, 2013; Cedergreen et al, 2012; Coors et al, 2012), toxicity assessment using combined effects models (Crépet et al, 2013; Hertzberg et al, 2013; Moser et al, 2012; Rider et al, 2008; Webster, 2013), evaluating stressor impacts environmentally (Allan et al, 2012; Florian et al., 2013; Løkke 2010), risk assessment studies (Johnson et al, 2013; Løkke et al, 2013; Meek, 2013; Moore and Teed, 2013) and examining chemical reactivity within complex mixtures (Goel et al, 2013). Although the specifics of such research vary, the common goal is improving the ability to predict the effects of exposure to chemical mixtures.…”

Proposal for environmental mixture risk assessment in the context of the biocidal product authorization in the EU

“…Obviously, if toxic compounds are not considered in a component based assessment, the calculated risk will be an underestimation of the actual risk of the biocidal product, see [25]. It is, however, impossible to provide a general estimate of the magnitude of such an underestimation, as this depends on the concentration and ecotoxicological potency of the compounds that are erroneously not included in the assessment.…”