Trophic fingerprinting of a pristine but rapidly deteriorating downstream region of a Western Ghats River

Chalakudy River is renowned for its pristine waters and rich ichthyofaunal biodiversity. The downstream area of the river is confronting a series of risks, including pollution, saline water ingression, sand mining, illegal and intensified fishing practices, and invasion of exotic and alien species. A mass balanced ecosystem model was constructed for the downstream region of Chalakudy River (DCR) using Ecopath with Ecosim (EWE), incorporating 12 functional groups to delineate the food web and network flow indices for the period 2020 to 2021. The trophic level (TL) of the ecosystem network ranged from TL-1 (detritus) to TL-3.4 (birds). High fishing pressure is one possible cause for the high ecotrophic efficiency values as evidenced by the fish groups. Both the grazing food chain and detritus food chain (detritivory: herbivory ratio 0.94) contributed more or less equal to the energy transfer between TL. Network analysis of the model indicated a mean transfer efficiency of 12%, with shares from primary producers (14%) and detritus (11%). A mixed trophic impact analysis demonstrated a strong positive impact of primary producers and detritus groups on most of the other ecological groups at higher trophic levels. The DCR model showed a high system throughput (32,464.7 t km-2 year-1), low system omnivory (0.09), low connectance index (0.36), low Finn's cycling index (4.9), and mean path length (2.8), low relative ascendency (37.5%), and high system overhead (62.5%). These indices propound that DCR is an immature and developing ecosystem with moderate strength in reserve to resist external perturbations.

Polycyclic aromatic hydrocarbons in the surface water and sediment along Euphrates River system: Occurrence, sources, ecological and health risk assessment

This study presented for the first time a comprehensive measurement campaign of 16 PAHs along the Euphrates River for five months, in both water and sediment samples. Our study revealed that the PAHs contamination increased along the flow direction due to the increasing non-point pollution and the return flows of agriculture. The 5-6 rings PAHs were dominant in water and sediment samples with an average of 42 % and 50 %, respectively. The diagnostic ratios of PAHs suggest that the pollution of these compounds originated mainly from petroleum product combustions. The carcinogenic PAHs formed 46 % and 55 % of the total measured compounds in water and sediment samples, respectively, which highlights potential ecological and human health risks. Based on sediment quality guidelines (SQGs), most sites exhibit an effect range between low and medium. The calculated incremental lifetime cancer risk (ILCR) for adult and children were in the 10^-2-10^-3 range, which is 3-6-fold higher than what was reported in the literature. These observations call for urgent attention from environmental authorities of countries sharing this key water source in Western Asia.

Polycyclic aromatic hydrocarbons in 30 river ecosystems, Taiwan: Sources, and ecological and human health risks

Polycyclic aromatic hydrocarbons (PAHs) are diverse contaminants of global concern because of their ubiquity, toxicity, and carcinogenicity to many organisms, including humans. This study determines the distribution and sources of PAHs in sediments and fish from 30 major rivers in Taiwan, and the risks these PAHs pose to river ecosystems and human health. The total concentrations of 26 PAHs in sediments and fish were 0.016-7.44 mg/kg dw and 0.096-5.51 mg/kg ww, respectively. The PAH composition in sediments differed from that in fish, indicating that sediments may not be the major contributor of PAHs to fish. The accumulation of different PAH compounds in fish was species-specific, depending on the lipid content, living pattern, and trophic level of each fish species, and on the level of environmental contamination. The diagnostic ratios revealed that PAHs in the sediment primarily originated from pyrogenic sources, with some contribution from petrogenic sources. The contribution of each source varied with the sampling site and season. Several water and air quality variables were found to significantly correlate with PAH concentration in sediments and fish, suggesting that PAHs were mainly derived from wastewater discharge and combustion emissions. The 95th percentile risk quotient values suggested that PAHs in sediment from six rivers pose high ecotoxicological risks. The toxic equivalents of benzo[a]pyrene for 16 PAHs in fish were 12-108 μg/kg dw. A human risk assessment using the 95th percentile values of hazard quotient, hazard index, and margin of exposure revealed that the consumption of contaminated fish muscle poses no remarkable risk to human health. However, the 95th percentile carcinogenic risk values indicated that benzo[a]pyrene concentrations in some fish muscles may pose a carcinogenic risk. Benzo[a]pyrene risk management measures are, therefore, necessary.