Biomonitoring potential of some local different terrestrial plants for monitoring polycyclic aromatic hydrocarbons (pahs) and heavy metal pollution

Abstract

In the current Anthropocene period of growing industrialisation and urbanisation, air pollution is one of the major issues confronting the globe. Most notably, heavy metal (HM) and polycyclic aromatic hydrocarbons (PAHs) pollution pose risks to public health as well as the environment. Thus, monitoring of HM and PAHs has become utmost necessary. But using traditional air monitoring methods is quite inconvenient because of their installation in large area, maintenance cost and manpower to handle. As a result, the alternate way to create a natural filtering barrier is to use green belts for biomonitoring of airborne contaminants. In this study, Jadavpur, a site of South Kolkata, is chosen as a study area based on pollution load data of CPCB and WBPCB. Two terrestrial plant species B. spectabilis and M. indica are chosen as biomonitors depending on their APTI value and abundance in the locality. B. spectabilis with APTI value >17 was found to be tolerant whereas M. indica with APTI value <17 found to be intermediately tolerant and can be bioindicator. The PAHs accumulation capacity and HM capturing capacity of both the plants are examined to establish the potential of the species in monitoring PAHs and HMs in and around the city. The relative water content (RWC), leaf extract pH, ascorbic acid, total chlorophyll content, protein, proline, sugar, wax, lipid, C, H, N, S, C/H, C/N content were determined to find the impact of PAHs and HMs on plant characteristics, which would help in identifying their tolerance potential and capturing capacity. Airborne PAHs and HMs were found to affect leaf biochemical and physiological parameters. For PAHs assessment, extractions were performed with toluene using Soxhlet extractor for 6 hrs. The samples were cleaned using silica gel column chromatography and analysed in HPLC. For metal concentrations, HMs were first extracted by digesting the sample in aqua regia for 24 hrs. The samples were then evaporated, filtered and analysed in ICP-OES. The findings revealed that both the plant species are good accumulators of PAHs (B. spectabilis: 198.82±3.66 μg g-1; M. indica: 358.86±0.09 μg g-1). The sources of PAHs were again determined by diagnostic ratios. NAPH, BghiP, DahA, PHEN and BaP were found to be the dominant PAHs in the studied location. The anthropogenic activities, vehicular emission, fossil fuel combustion were the major contributors of PAHs in that area. Among all the PAHs found, 96-97% are carcinogenic and mutagenic (as determined from carcinogenic and mutagenic equivalent concentrations (BaPTEQ and BaPMEQ)), having serious health impacts on human being. Based on HM accumulation, MAI was found higher in M. indica (35.11) than B. spectabilis (29.68). Ni, Zn, Pb, Cu, Cr, Al were the major HMs found in the area. The plant species showing high MAI value and high APTI value are suitable for planting where HM and PAHs pollution is higher and can be used to build green belt in and around the city for biomonitoring of PAHs from the air.