An integrated approach to study the risk from landfill soil of Delhi: Chemical analyses, in vitro assays and human risk assessment

In the present study, landfill soil of three municipal solid waste landfill sites of Delhi, India were toxicochemically analyzed for human risk assessment as inadequate information is available on the possible health effects of the contaminants present in landfill soil. The landfill soil samples were prepared for analyzing heavy metal concentration, organic contaminants and toxicity analysis separately. Composite soil sample collected from three landfill sites were analyzed for heavy metal by ICP-AES. Metal concentration so obtained was below the permissible limit of soil but higher than the set limits for effluent. Some of the persistent organic contaminants like phthalates, benzene derivatives, halogenated aliphatic compounds and PAHs derivatives were detected by scan mode GC-MS. Further, concentration of 17 polycyclic aromatic hydrocarbons (PAHs) in landfill soil of Delhi was evaluated by selective ion monitoring GC-MS in order to ascertain their contamination levels and potential health risk. The concentration of total PAHs in the samples ranged from 192 to 348 mu g/kg. The maximum concentrations of PAHs were found in Ghazipur landfill site followed by Okhla and Bhalswa landfills. Cancer risk (CR) values of sampling sites were within the acceptable range for adults, adolescents and children (both male and female) suggesting that PAHs present in landfill soil are unlikely to pose any cancer risk for population based on dermal contact, ingestion and inhalation exposure pathways. However, landfill soil organic extract showed significant cytotoxic and genotoxic effects on HepG2 cell line as revealed by MTT and Comet assays respectively. The observed MTT EC50 values ranged from 7.58 to 12.9 g SedEq/Lalong with statistically significant DNA damage. Thus, although the soil organic extract contained low concentrations of PAHs with negligible carcinogenic potential, but the mixture of organic pollutants present in soil were found to be toxic enough to affect human health due to their synergistic or additive actions.