Assessment of genotoxic and tumorigenic potential and heavy metal contamination in roadside soil and plants of Amritsar (Punjab), India

Vehicular pollution may end in the bioaccumulation of various toxic metals in soil and consequent genetic changes in roadside plants. To check this hypothesis, the present study was performed to evaluate the seasonal dependence (pre- and post-monsoon) of the genotoxic (Allium cepa root chromosomal aberration assay) and tumorigenic (Potato disc tumor assay) potential; and heavy metals contamination of roadside soil and plant samples (Alstonia scholaris; Nerium oleander; Tabernaemontana divaricata and Thevetia peruviana) collected from different traffic density areas of Amritsar city, Punjab, India. The index of geo-accumulation and bio-concentration factor were also calculated to determine the contamination level; and absorption and bioaccumulation of heavy metals in soil and plant samples, respectively. Genotoxicity, in terms of percent chromosomal aberrations, was dominated by delayed anaphases followed by stickiness, bridges, vagrants, C-mitosis, and breaks. The highest genotoxicity was induced by roadside soil from a heavy traffic site, the lowest by soil from a zero traffic site. Tumorigenicity, in terms of tumors were induced maximum by mixtures of soil extracts with bacterial culture for metabolic activation as compared to only water soil extracts during pre- and post-monsoon samples. The trend of heavy metal contents in leaf samples was found to be iron (Fe) > chromium (Cr) > manganese (Mn) > cobalt (Co) and for soil samples it was found to be Fe > Mn > Cr > Co. Index of Geo-accumulation revealed moderate contamination of the study area by heavy metals whereas Bio-concentration factor showed both absorption and accumulation of Fe, Cr and Co (BCF > 1) in leaf samples except for Mn (BCF < 1). The present study revealed high genotoxicity and tumorigenicity in soil samples which suggested plant bioassays as useful tool for monitoring and risk evaluation of soil pollution. Our study showed that heavy metal stress affected the cell division thereby inducing chromosomal aberrations and tumor growth.