Characterization of toxicants in urban road dust by Toxicity Identification Evaluation using ostracod Heterocypris incongruens direct contact test

Abstract

The current study involves characterization of organic compounds, heavy metals, and ammonia as potential toxicants in one arterial road (St. 3) and two highway (St. 7 and 8) urban road dust (URD) collected in Tokyo, Japan. URD toxicity was evaluated by Toxicity Identification Evaluation using the ostracod Heterocypris incongruens direct contact test. URDs were treated with resins (10% XAD-4, 20% SIR-300 and 20% SIR-600) to determine the reduction in mortality after treatment. The mortality of ostracods exposed to St. 3 URD (baseline 80%) was significantly (p<0.05) reduced to 0% and 47% after XAD-4 and SIR-300 treatment respectively. This reduction led us to suspect hydrophobic organic compounds and heavy metals as potential toxicants. Subsequent elution of the recovered XAD-4 with polar (methanol, acetone) and non-polar (dichloromethane) solvents confirmed the dominance of relatively polar hydrophobic organic toxicants. The dissolved concentration of Cu and Zn after SIR-300 treatment exceeded the 50% lethal concentration (LC50) for ostracods, which led us to suspect Cu and Zn as other probable toxicants. The concentration of Zn in a SIR-300 acidic elutriate, recovered after the termination of toxicity test, confirmed Zn as one of the toxicants in St. 3. The baseline mortality (100%) of St. 7 was significantly reduced (23%) by SIR-300 treatment. This indicated the presence of heavy metals as the probable toxicant. However, the concentration of dissolved heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) in the overlying water was below previously reported LC50 values for each metal in St. 7. Recovery of Zn concentrations exceeding the LC50 in the St. 7 SIR-300 elutriate led us to suspect a dietary exposure route of Zn to the ostracod during the direct contact test. The overall results indicate that the toxicant types can vary widely depending on the road sampled.