Incorporating benchmark dose into sediment toxicity testing using zebrafish (Danio rerio)

Mortality is the most common endpoint surveyed for environmental risk assessment of sediment contaminated with organic pollutants. More recently, a modified zebrafish embryo toxicity assay (zFET) has been utilized in sediment toxicity assessments as it provides data on both mortality and distinct malformations associated with the whole sediment and sediment extract containing only the organic pollutants. Taking this approach further, we herein have incorporated benchmark dose (BMD) calculations through EPA's BMD software based on zebrafish mortality and malformation data; thus, providing a framework to apply this methodology to sediment toxicity assessments. The goal of this study was to assess relative toxicity of sediment chemical extracts using a zfBMD approach based on mortality, malformation and behavior as compared to hazard index calculations from chemical analysis. To perform this study, sediment from the Lower Rio Grande Valley of Texas resacas 'oxbow lakes', were collected to assess utility of this approach in sediment toxicity assessments. Chemical analysis of 95 organic contaminants revealed the presence of 45 organic pollutants in sediment extracts from 13 locations and 5 resacas across four sampling events in a one-year period to determine seasonal variability. Our results indicated that the zfFET assay was correlated with seasonal applications of pyrethroids, neonicotinoids and organophosphates. Incorporating BMD for the three endpoints allowed for better representation of sub-acute toxicity as many of the sediment extracts induced malformations and behavior changes at concentrations below the chemical bioavailable concentration in the sediment. Results of this study will aid in the development of utilizing fish embryo-larvae BMD mortality and malformation calculations in ecological risk assessments of contaminated sediments.