Ecotoxicity of xanthene dyes and a non-chlorinated bisphenol in soil

Abstract

Soil eco-toxicity testing was conducted in support of Canada’s Chemical Management Plan (CMP) to fill data gaps for organic chemicals known to primarily partition to soil, and of which the persistence and inherent toxicity are uncertain. Two compounds representative of specific classes of chemicals: non-chlorinated bisphenols containing an –OH group (4,4′-methylenebis(2,6-di-tert-butylphenol (Binox)) and xanthene dyes (2′,4′,5′,7′-tetrabromo-4,5,6,7-tetrachloro-3′,6′-dihydroxy-, disodium salt (Phloxine B), 2′,4′,5’,7′-tetrabromofluorescein (TBF), 4′,5′-dibromofluorescein (DBF), and 4,5,6,7-tetrachlorofluorescein (TCF)) were evaluated. The effect of these substances on plant growth (Elymus lanceolatus and Trifolium pratense) and soil invertebrate survival and reproduction (Folsomia candida and Eisenia andrei) were assessed using a field-collected sandy soil. Binox was persistent throughout testing (up to 63d) with an average recovery of 77±2.9% at test end. Binox was not toxic to plants (IC50s>1076mgkg−1) or E. andrei (IC50s>2651mgkg−1); however, a significant reduction in F. candida adult survival and reproduction (IC50=89 (44–149) mgkg−1) was evident. Phloxine B was also persistent throughout testing, with an average recovery of 82±3.0% at test end. Phloxine B was significantly more toxic than Binox, with significant reductions in plant root growth (IC50s⩾11mgkg−1) and invertebrate reproduction (IC50s⩾22mgkg−1). DBF toxicity was not significantly different from that of Phloxine B for plant root growth (IC50s⩾30mgkg−1), but was significantly less toxic for shoot growth (IC50s⩾1758mgkg−1), and invertebrate adult survival (IC50s⩾2291mgkg−1) and reproduction (IC50s⩾451mgkg−1). A comparison between all four xanthene dyes was completed using F. candida, with the degree of toxicity in the order of Phloxine B⩾TBF∼DBF>TCF. The results from these studies will contribute to data gaps for poorly understood chemicals (and chemical groupings) under review for environmental risk assessments, and will aid in the validation of model predictions used to characterize the fate and effects of these substances in soil environments.