Bioavailability and risk assessment of trace metals in sediments of a high-altitude eutrophic lake, Ooty, Tamil Nadu, India

Biochar-enhanced bioremediation of eutrophic waters impacted by algal blooms

The permanent problem of formation of algal blooms in water polluted with nitrogen and phosphorus is one of the formidable environmental problems. Biochar has the potential to solve the issues related to eutrophication due to its special structure and ability to absorb the nutrients. Biochar's exceptional nutrient absorption capacity allows it to absorb excess nutrients, causing the algae to use fewer nutrients. This review deals with effective performance of biochar in reducing the effects caused by algal blooms and improving the environmental conditions. Besides, an analysis of the issues involved addresses the origins and consequences of nitrogen and phosphorus pollution, and the formation of algal blooms is also reviewed. It then delves deeply into biochar, explaining its properties, production methods, and their uses in environmental contexts. The review emphasizes that biochar can be effective in dealing with many challenges associated with environments affected by algal blooms, specifically focusing on the positive effects of biochar and algae to examine their roles in controlling algae growth. Finally, the review emphasizes new achievements and innovative ideas to foster sustainable aquatic ecosystems. The discussions emphasize the central role of biochar in managing nutrient-rich waters and algal blooms.

Heavy metal analysis of water and sediments of the Kaptai Lake in Bangladesh: Contamination and concomitant health risk assessment

In this study, concentrations of 9 heavy metals (Cr, Fe, Co, Ni, Cu, Zn, As, Cd, and Pb) in water and sediments of the Kaptai Lake were determined by neutron activation analysis and atomic absorption spectrometry techniques to study their distribution and contamination in the lake. Average concentrations of Cr and Co in sediments, and Fe and Pb in water were higher than those of some international guideline values. Different environmental pollution indexes (individual and synergistic) suggested that the sediments of Kaptai Lake are minorly enriched by As and Zn, and have low severity of contamination at most of the sampling sites. For residential receptors exposed to the heavy metals in lake water, both non-carcinogenic and carcinogenic hazards were assessed which indicated that there is no carcinogenic risk for As while Cr shows a slightly carcinogenic risk. Moreover, estimated potential ecological risks and different SQGs suggested low ecotoxicological risks in the sediments of Kaptai Lake. Multivariate statistical analyses revealed the correlation among the studied heavy metals and indicated that the origin of most of the metals is mainly lithogenic and a small number of metals (Cu and Pb) from anthropogenic sources. The results of this study will be helpful in developing a pollution control strategy for the lake.

Metal bioavailability, bioaccumulation, and toxicity assessment through sediment and edible biota from intertidal regions of the Aghanashini Estuary, India

The sediment cores and edible biota from the intertidal regions of the Aghanashini Estuary were studied for the assessment of metal toxicity. The estuarine sediments received natural input of metals through the weathering of Dharwar and peninsular gneisses, and laterites. The sediments were enriched in Fe, Mn, Zn, Cu, Co and Ni than the upper crustal value. Also, the concentration of Fe, Zn, Cu, Co and Ni was more in the Aghanashini Estuary than other estuaries around the world. The Enrichment Factor (EF) revealed enrichment of Zn, Cu, Co and Ni in sediments, while the Geo-accumulation Index (Igeo) exhibited unpolluted-moderately-strongly polluted class of Fe, Zn, Cu, Co and Ni. The enrichment and pollution of metals in sediments was due to anthropogenic sources (domestic sewage, aquaculture and agricultural discharge) in the estuary. The presence of metals at a high concentration in the residual fraction and at a significant proportion in the bioavailable fractions construed both natural and anthropogenic sources of metal, and their bioavailability in the estuary. The physico-chemical factors (ionic composition, H+ ions, redox potential, and microbial activity) regulated the adsorption and desorption of metals in sediments. The Screening Quick Reference Table (SQUIRT) revealed level of bioavailable Mn and Co higher than the Apparent Effects Threshold (AET) and thus, indicated adverse toxic effects on biota. The Risk Assessment Code (RAC) indicated medium-high-very high risk of Mn, Zn, Co, Cu and Ni to biota. Also, the concentration of Fe, Mn, Zn, Cu and Ni in biota was in excess of permissible limit which pointed to their toxicity to biota and their consumers. The Target Hazard Quotient (THQ) value > 1, and Hazard Index (HI) value > 10 revealed risk of metal toxicity to humans.

Mobility and risk assessment of heavy metals in benthic sediments using contamination factors, positive matrix factorisation (PMF) receptor model, and human health risk assessment

Metal pollution in benthic sediments was fractionated and modelled to quantify the risk of anthropogenic activities on river ecosystems. In this study, the individual contamination factor (ICF) and the global contamination factor (GCF) were used to measure the contamination levels in the sediments. On the other hand, the mobility factor (MF) was used to quantify the mobility of heavy metals in benthic river sediments. The factors used to assess pollution in benthic sediments employ bioavailable fractions of heavy metals, which have a greater chance of release into aquatic sediments and hence are more dangerous to the environment. Heavy metal mobility (MF) is highest in the post-monsoon season for Zn, Pb, Cu, and Co; Fe in winter; Mn in pre-monsoon; and Cd in monsoon. This means that heavy metals accumulate in benthic sediments during the post-monsoon season when river flows are less turbulent. ICF and GCF data show that pollution levels are higher post-monsoon than the rest season levels. Sediment samples were further subjected to the positive matrix factorization (PMF) model, which identified four factors that explained the variation in the study: factor 1 is concerned with anthropogenic Cu, Cd, and Co pollution, while factors 2, 3, and 4 are concerned with Fe, Mn, and Zn pollution. Finally, the total cancer risk (TCR) and hazard index (HI) are employed to quantify the risk to human health from accidental ingestion and dermal exposure. According to the risk outcomes from probabilistic and deterministic approaches, river exposure is dangerous to human health, with dermal absorption being the most significant concern of the exposure paths.