After confirmation of the toxicity of St. 3 URD, XAD-4 was recovered from each test well by wet sieving. The XAD-4 recovery (XAD-4 recovered after toxicity test/XAD-4 added in each test plate) varied from 88 to 96% in wt. basis. Elution of Purmorphamine organic compounds from XAD-4 resin was performed with two polar solvents, methanol (MeOH) and acetone, and a non-polar solvent dichloromethane (DCM). These solvents were selected based on their octanol water partitioning coefficient. Elution was done twice with 5 ml of MeOH. After the recovery of MeOH, the same XAD-4 sample was eluted twice with 5 ml of DCM. These elutriates were marked as MeOH and MeOH → DCM respectively. A fresh sample of recovered XAD-4 was similarly eluted with DCM and DCM followed by MeOH (DCM → MeOH). This process was repeated with acetone and acetone followed by DCM (Acetone → DCM) to a fresh batch of recovered XAD-4. The elution was done manually in a batch process by mixing the solvent and resin in a glass tube, holding for 1 h, and then separating the solvent from the resin by vortexing for approx. 15–30 s. The elutriates were then concentrated by gentle purging with N2 near to dryness around 30 °C. The color of the final concentrate was light green to somewhat opaque with precipitate for the resin treated URD samples whereas the concentrate from clean XAD-4 (operational control) was watery (same as solvent color) and transparent for each solvent elution. The precipitates in samples were dissolved by boiling (~ 40 °C) with DCM. In some cases all of the precipitates could not be completely dissolved. The concentrate was dissolved in dimethyl sulfoxide (DMSO) to a final volume of 100 μl. For the purpose of water-only toxicity testing, the DMSO concentration in each test well was adjusted to 0.5–0.6%, v/v. Each test well contained organic compound equivalent to that obtained from 1 ml of road dust. An additional toxicity test with dose response of DMSO was also conducted so as to confirm the residual toxicity of DMSO, if any.