Assessment of pollution and risks associated with microplastics in the riverine sediments of the Western Ghats: a heritage site in southern India.

There is very little knowledge on microplastic pollution in the Western Ghats (WG), a heritage site in southwest India. To address this, we have studied the spatiotemporal variations of sedimentary microplastics (MPs) from the River Sharavathi, a pristine river in the Western Ghats (WG), southern India. The rich biodiversity in the region makes it relevant to analyse the distribution of this emerging pollutant that is causing harm to the biota and the ecosystem. We analysed the sedimentological and carbon content (organic and inorganic) of these sediments and explored their relationship with MPs. Finally, risk assessment indices such as the Pollution Load Index (PLI), the Polymer Hazard Index (PHI), and the Potential Ecological Risk Index (PERI) were calculated to detect the levels of plastic pollution. The concentration of MPs ranged from 2.5 to 57.5 pieces/kg and 0 to 15 pieces/kg during the pre-monsoon and post-monsoon seasons, respectively. The dip in the MPs' abundance during the post-monsoon season was due to the extremely high rainfall in the river basin during July-August 2019, which would have entrained the sedimentary MPs and transported them to the coast/Arabian Sea. Smaller MPs (0.3-1 mm) were more abundant than the larger MPs (1-5 mm), mainly due to the breakdown of sedimentary plastics by physical processes. Fragments, films, foams, and fibres were the main categories of MPs, and the main polymers were polyethylene, polyethylene terephthalate, and polypropylene. No significant relationship was observed between the sedimentological properties and microplastics, which may be due to the different physical properties of sediments and microplastics. The PLI, PHI, and PERI indices suggest different contamination levels in the river basin. Based on the PLI scores, all the samples belong to the hazardous level I suggesting minor risk category, and the risk of microplastic pollution falls under the high to hazardous risk category based on the PHI values. The PERI value ranged from 160 to 440 and 40 to 2240 during the pre-monsoon and post-monsoon seasons, respectively. The risk assessment in a region known for its rich biodiversity is crucial, as the data can be used by the district administration to mitigate plastic pollution.

Risk assessment and spatio-temporal distribution of dissolved trace metals in Swarna, Sharavati and Kali estuaries, South-West Coast of India.

Trace metals act as a limiting nutrient and prerequisite for primary productivity in marine environments. The distribution of metals in dissolved phase along the salinity gradients of Swarna, Sharavati and Kali estuaries in southwestern India, during post and pre-monsoon seasons, were studied. We have investigated the behaviour of trace metals in the estuarine environment and their extent of impact on human health and ecosystem. The study revealed, non-conservative behaviour of dissolved Mn, Fe, Ni, Cd and Co in the estuaries. Whereas Cu behaved non-conservatively in post-monsoon and conservatively in pre-monsoon seasons. Risk assessment studies revealed that higher chronic daily intake (CDI) in humans, through dermal pathway, in Swarna and Sharavati estuaries during post-monsoon, whereas it was during pre-monsoon season in the Kali estuary. Hazard Index values for the studied metals in adults and children are below risk thresholds, though children are more prone to health risk through the dermal pathway.

Study of trace metal contamination and ecological risk assessment in the sediments of a tropical river estuary, Southwestern India.

The present study aims to assess the extent of trace metal pollution in the sediments of Sita-Swarna estuary, west coast of India, and investigate their possible ecological risk on the aquatic environment. The sediment cores were analyzed for sand, silt, clay, organic carbon, and trace metals (Al, Fe, Mn, As, Cd, Co, Zn, Pb, Ni, Cr, and Cu) at 2-cm intervals. The study revealed that sediments have deposited in relatively violent to very violent hydrodynamic energy conditions. Factor analysis indicated that the metal distribution is mainly controlled by Fe-Mn oxyhydroxides and organic carbon. Further, the geochemical approach, pollution indices, and statistical evaluation revealed moderate pollution in the catchment. From an ecotoxicological perspective, the estimated risk index (RI) value was found to less than 150, indicating low risk for aquatic life. Thus, this baseline study would help to adopt strategies in pollution control and protect the fragile marine environment.

Dissolved carbon and silica fluxes from Kali, Sharavati and Sita-Swarna rivers, Southwestern India.

Spatio-temporal behaviour of dissolved organic carbon (DOC), inorganic carbon (DIC) and silica (DSi) along the salinity gradient of three south-west Indian monsoonal estuaries are presented. This study showed both conservative and non-conservative behaviour of DOC along the salinity gradient under varying physico-chemical conditions. The gross flux of DOC arriving at the estuary from the rivers was estimated as 0.9 × 109 g/yr for Sita-Swarna river, 4.2 × 109 g/yr for Sharavati river and 5.6 × 109 g/yr for Kali river. Similarly, the net fluxes of DOC estimated beyond the estuarine zone was 5.5 × 109 g/yr (Sita-Swarna), 8.0 × 109 g/yr (Sharavati) and 7.7 × 109 g/yr (Kali). This indicates that these estuaries are the sources of organic carbon to the ocean. The DIC linearly increased towards the higher salinity with net fluxes of 38 × 109 g/yr (Sita-Swarna), 75 × 109 g/yr (Sharavati) and 97 × 109 g/yr (Kali). The combined DIC flux of Sita-Swarna, Sharavati and Kali rivers is ~8% of the total DIC fluxes received from the west flowing rivers of India, to the Arabian Sea. The DSi showed a biogenic removal of 80-85% in all the studied estuaries. From this study it is concluded that the west flowing river estuaries are net sources of DOC and DIC and net sink for DSi. Consideration of the role of west flowing rivers of peninsular India is important for the better understanding of the carbon dynamics in the river-estuary-ocean boundary.