Fly ash generated by TPPs is one of the ways mercury is released into the environment. Fly ash is usually disposed in ash ponds in the form of ash slurry, forming an aquatic ecosystem of its own
A new study found mercury (Hg) in birds concentrated around two thermal power plants (TPP) in Maharashtra’s Nagpur could lead to bioaccumulation and biomagnification. Bioaccumulation is the gradual accumulation of substances, such as pesticides or other chemicals, in an organism, while biomagnification is the concentration of a toxin in the tissues of organisms at successively higher levels in a food chain
Traces of Hg on the feathers of the avifauna (birds of a particular region) in this area was linked to the Hg present in the ash ponds of the TPPs. Coal-based TPPs are the major source of mercury — the ninth most toxic element found on earth — emissions into the environment. Mercury contributed over 80 per cent of emissions released by the TPPs, according to 2016 estimates by Delhi-based think-tank Centre for Science and Environment.
Fly ash generated by TPPs was one of the ways through which Hg was released into the environment. Fly ash is usually disposed in ash ponds in the form of ash slurry, forming an aquatic ecosystem of its own.
In a wetland, Hg was found in two forms: organic (MeHg) and inorganic (iHg). MeHg has more bioconcentration than its counterpart, resulting in bioconcentration — the process by which a chemical concentration in an aquatic organism exceeds that in water — and subsequent physiological, reproductive and behavioral changes.
The aim of the research — published in journal Environmental Monitoring and Assessment April 2, 2020 — was to understand the presence of toxic Hg in native and migratory avifaunal species found in the wetlands near Koradi, a 620 MW TPP and Khaparkheda, a 880 MW TPP in Nagpur.
A non-invasive method of monitoring — that suggested comprehensive and regular monitoring of the toxic contaminants in the food chain — emerged and was deemed important by the study. Samples of fly ash, soil, water and plants were also analysed to support the study.
The study was conducted in three ash ponds located near the two TPPs and were marked KI, K2, and K3.
Fly ash samples
The Hg in six fly ash samples collected from the ash ponds showed one of the samples belonging to the Koradi TPP had the most amount of it. The least amount was from the Khaparkheda TPP. The amount of Hg in all the samples, thus, were below the permissible amount.
The seven soil samples from the two TPP locations showed all three samples of Khaparkheda TPP had the greatest levels of Hg in them. The amount of Hg for five of the seven samples was higher than the maximum permissible limit of 0.05 parts per million (ppm) set by the World Health Organization and the Bureau of Indian Standards.
The cause for this could be the sticking of Hg with the organic component of the soil and subsequently not allowing it to seep to the nearest water bodies.
The amount of Hg in the seven collected water samples was below permissible standards of 0.001 ppm. This could be because of neutralised fly ash contaminants in water that contributed to the low formation of monomethyl Hg.
Plants samples from 16 species growing in and near ash dykes — including Typha laitfolia, Croton bonplandianum, Prosopis juliflora — were collected. The Hg present in these plants was well below the permissible standard. The little concentration of Hg in the plants could have been brought in by the Hg present soil through root uptake.
This also hinted at the potential of phytoremediation techniques to reduce the toxic Hg from the soil.
Hg in Bird feathers samples
Bird feathers sample of eight bird species, like Indian pond heron, darters, Moorhen, etc, were collected and observed. It was seen that some of the species had a higher concentration of Hg.
This could be because of feeding on fishes and insects in ash ponds. A majority of the bird species, however, had extremely low traces of Hg. In conclusion, it was seen that except in soil, other samples collected from fly ash, plants, water and bird feathers had low quantities of Hg in them.
The purpose of the study was to establish new ways to analyse the presence of toxic elements like Hg. One such unique method was the non-invasive biomonitoring of bird feathers. Bird feathers turned out to be an ideal specimen, as they did not hurt the organism or require the physical presence of the bird.
In 2018, the Union Ministry of Environment, Forest and Climate Change claimed all units of TPPs will be able to comply with Hg emission standards once the required technologies are installed.
These technologies include Flue-gas desulfurisation (FGD), electrostatic precipitators (ESP), and selective catalytic reduction (SCR). Technologies to monitor Hg emissions specifically, however, were not mandated. If plants fail to install FGDs, ESPs, and SCR, monitoring Hg will become difficult.
Coal-fired TPPs are the major source of electricity in India. While these anthropogenic activities contribute to the development of our country, it also added to environmental degradation.
In the longer run, regular monitoring by TPPs, along with finding different strategies to understand the levels and impact of toxins like Hg in the ecosystem, can help find solutions and avoid future pitfalls.
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