Polycyclic aromatic hydrocarbons (pahs) in particulate phase (adsorbed) and mesophyll tissue phase (absorbed) of the leaves of a wetland plant bioindicator: a focus on distribution, risk assessment, and sources

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are persistent and resistant to bio-degradation and making them lipophilic environmental carcinogens with detrimental effects on public health. Considering PAHs as priority pollutants, their distribution in soil of the studied area was investigated. The result revealed that the investigating area is highly polluted with soil PAHs (283.14 µg g¹) contamination. The comparison of soil PAHs pollution level with sediment quality guidelines (SQGs) including the effect range low (ERL) and effect range medium (ERM) values, indicating adverse biological effects on the research region ecosystem. Using M-ERM-Q (mean effect range medium-quotient) and M-PEL-Q (mean probable effect level-quotient) in the situation, the biological risk or anticipated combined toxicity for exposure to a mixture of PAHs in the soil was assessed which again implies toxicological effects to the aquatic creatures to the studied area. Additionally, risk quotient (RQ) were used to assess the ecological risk that pollutants provide to aquatic biota, where RQ-PAHS(NCS) <800 and RQ-PAHS(MPCS) >1 in the research locations suggest low to moderate and high levels of ecological risk, respectively. This finding led to urgent biomonitoring of PAHs pollution in the study area (Panchasayar Lake in South Kolkata). Moreover, research on the biomonitoring of Particulate matter (PM) and PAHs pollution in wetland has been lacking up until the date. Panchasayar Lake in South Kolkata, India is considered as study site in the present study, and it was selected based on WBPCB pollution load data. In this context, two wetland plant species namely Mikania micrantha kunth and phyla nodiflora (L.) Greene was selected as bio-monitoring species based on air pollution tolerance index (APTI). The species called phyla nodiflora (L.) Greene was found to be intermediately tolerant and potential bioindicator, while Mikania micrantha kunth was found to be tolerant with APTI value > 17 with expected biomonitoring potential. To ascertain the influence of PAHs pollution load on the chosen plant species some physical and biochemical properties are assessed relative water content (RWC), pH of the leaf extract, ascorbic acid, total chlorophyll content, protein content, proline content, sugar content, wax, and lipid content. To evaluate the presence of PAHs in soil and both bioindicator plant species, six hours of toluene extractions were carried out using a Soxhlet extractor. Both the studied plant species were found to be effective PAHs accumulators, according to the research findings (Mikania micrantha kunth: 161.74 µg g¹ and Phyla nodiflora (L.) Greene: 209.04 µg g¹). Using diagnostic ratios, the contribution of various sources of PAHs in the ambient were checked and confirmed. Vehicular emissions, anthropogenic activities, and the combustion of fossil fuels are found to be the major responsible factors. High levels of PAHs have been found to be carcinogenic and mutagenic (as shown by their carcinogenic and mutagenic equivalent concentrations, or BaP-TEQ and BaP-MEQ) and have been linked to major health effects in humans. Additionally, Particulate matter captured by both the plant species and their associated PAHs levels were investigated in this work, where BaP, NAPH, BghiP, BbF, BkF were identified mainly sourced from vehicular and diesel/gasoline emission. High accumulation level of PAHs in these plant species suggested them as suitable bio-monitor to assess the PAHs pollution status in the study area and for further remediation activities to ensure environment sustainability.