Diffusive mass flux of different polycyclic aromatic hydrocarbons (PAHs) and estimation of lifetime average daily dose in a soil micro-block system

Abstract

The polycyclic aromatic hydrocarbons (PAHs) are widely distributed in the environment, highly persistent to degradation, and remained in any system for an extended period. Their distribution in a soil system depends upon soil properties and the nature of PAH itself. Therefore, an experiment was conducted in the soil-block system to evaluate the release, transport, toxicity equivalents, and lifetime average daily dose (LADD) of different PAHs over 30 days by growing maize (Zea mays L.) plants. The soil was spiked at the rate of 500 ppb by different PAHs in soil-block systems from one side. After spiking, soil sampling was performed from four different distances {10, 20, 30, and 40 mm distance from the source (DFS)} in three intervals (5, 15, and 30 days) of time. Results depicted that the maximum diffusive mass flux (Jd) was obtained at 0–10 mm DFS after five days of sampling for all PAHs and a minimum from 30 to 40 mm DFS after 30 days of sampling. Out of all PAHs concentrations, three PAHs concentrations were in detectable range and high as compared to other PAHs. The fluoranthene was released maximum as compared to pyrene, and benzo[k]fluoranthene at all time interval samplings with and without plants. The concentration of all PAHs release was highest where plants were grown as compared to the samples obtained where no plants were grown. The growth of maize under PAHs application enhanced diffusion as compared to control (where no plants were grown). The LADD after 5 days of sampling was highest at 0–10 mm DFS as compared to 10–20 mm, 20–30 mm, and 30–40 mm DFS. Benzo[a]pyrene toxicity equivalency (BaPTEQ) data for fluoranthene, pyrene, and benzo (k)fluoranthene showed a range from 0.001 to 0.299 ng m3, 0.001–0.182 ng m3 and 0.001–0.202 ng m3, respectively. It was concluded that the presence of plants in a soil enhanced the diffusive mass flux of PAHs but also increased the LADD and BaPTEQ.