Temporal evolution of polycyclic aromatic hydrocarbons in sediments of the Hooghly river, West Bengal, India

The study evaluated the effect of monsoons on the levels of polycyclic aromatic hydrocarbons in the Hooghly River estuary sediments over 2018–2021. It was observed a cyclical enrichment of organic material, carbonate deposits, and clay over the post-monsoon and impoverishment over the monsoon because of the heavy rains and flood events. The mean total level of polycyclic aromatic hydrocarbons was 1682 ng/g with a wide range of variability depending on the season, 125–6518 ng/g, higher than previous assays and lower than a contemporary survey. Also, there was a marked predominance of the polycyclic aromatic hydrocarbon heavy pool, ~ 83%, with fluoranthene and pyrene making more than 40% of the total hydrocarbons loads and with a large variability of the composition with the monsoon. Concerning the numerical sediment quality guidelines, the mean individual compound levels, and ∑PAHs, do not surpass effect range low, effect range median, and apparent effects threshold limits and keep fairly below thresholds with no evidence of detrimental biological consequences. Temporal trends of polycyclic aromatic hydrocarbons split over two periods after the 2019 monsoon, with a sudden drop in hydrocarbon levels from two times for naphthalene, acenaphthylene, pyrene, benzo(a)anthracene, chrysene, to 6–7 times for phenanthrene, benzo(b)fluoranthene, benzo(a)pyrene, and indeno[1,2,3-cd]pyrene, with an overall decrease of ∑PAHs of threefold from 2948 to 959 ng/g. Monsoon seems to play as a sort of natural attenuation effect, slowing down river decline.