Soil concentrations, occurrence, sources and estimation of air–soil exchange of polychlorinated biphenyls in Indian cities

Past studies have shown potentially increasing levels of polychlorinated biphenyls (PCBs) in the Indian environment.
This is the first attempt to investigate the occurrence of PCBs in surface soil and estimate diffusive air-soil
exchange, both on a regional scale as well as at local level within the metropolitan environment of India. From the
north, New Delhi and Agra, east, Kolkata, west, Mumbai and Goa and Chennai and Bangalore in the southern India
were selected for this study. 33 PCB congeners were quantified in surface soil and possible sources were derived
using positive matrix factorization model. Net flux directions of PCBs were estimated in seven major metropolitan
cities of India along urban-suburban-rural transects. Mean Σ33PCBs concentration in soil (12 ng/g dry weight)
was nearly twice the concentration found in global background soil, but in line with findings from Pakistan and
urban sites of China. Higher abundance of the heavier congeners (6CB–8CB) was prevalent mostly in the urban
centers. Cities like Chennai, Mumbai and Kolkata with evidence of ongoing PCB sources did not show significant
correlation with soil organic carbon (SOC). This study provides evidence that soil is acting as sink for heavy
weight PCB congeners and source for lighter congeners. Atmospheric transport is presumably a controlling factor
for occurrence of PCBs in less polluted sites of India.