Heavy metal toxicity has proven to be a major threat and there are several health risks associated with it. The toxic effects of these metals, even though they do not have any biological role, remain present in some or the other form harmful for the human body and its proper functioning. They sometimes act as a pseudo element of the body while at certain times they may even interfere with metabolic processes. Few metals, such as aluminium, can be removed through elimination activities, while some metals get accumulated in the body and food chain, exhibiting a chronic nature. Various public health measures have been undertaken to control, prevent and treat metal toxicity occurring at various levels, such as occupational exposure, accidents and environmental factors. Metal toxicity depends upon the absorbed dose, the route of exposure and duration of exposure, i.e. acute or chronic. This can lead to various disorders and can also result in excessive damage due to oxidative stress induced by free radical formation. This review gives details about some heavy metals and their toxicity mechanisms, along with their health effects.

https://sciendo.com/pdf/10.2478/intox-2014-0009

Toxicity, mechanism and health effects of some heavy metals

Urban woodlands: their role in reducing the effects of particulate pollution.

Rice agriculture feeds about a third of the world's population. However, rice fields are also an important source in the global budget of the greenhouse gas methane. The emission of methane from flooded rice fields is the result of the activity of methanogenic archaea that produce the methane and of methanotrophic bacteria that oxidize part of it, so that the ecology of these two physiological groups of microorganisms is key for the understanding of methane cycling in rice fields and for possible mitigation of emission from this important agro-ecosystem. In this chapter I will describe the ecology of methanogens and methanotrophs and will give examples where production and emission of methane on the field scale can be understood on the basis of processes on the microscale.

Microbial Ecology of Methanogens and Methanotrophs

Chromium (Cr) is the second most common metal contaminant in ground water, soil, and sediments due to its wide industrial application, hence posing a serious environmental concern. Among various valence states, Cr(III) and Cr(VI) are the most stable forms. Cr(VI) is the most persistent in the soil and is highly toxic for biota. Since Cr is a non-essential element for plants, there is no uptake mechanism; Cr is taken up along essential elements such as sulfate through sulfate transporters. Cr accumulation in plants causes high toxicity in terms of reduction in growth and biomass accumulation, and Cr induces structural alterations. Cr interferes with photosynthetic and respiration processes, and water and minerals uptake mechanism. Various enzymatic activities related to starch and nitrogen metabolism are decreased by Cr toxicity either by direct interference with the enzymes or through the production of reactive oxygen species. Cr causes oxidative damage by destruction of membrane lipids and DNA damage. Cr may even cause the death of plant species. Few plant species are able to accumulate high amount of Cr without being damaged. Such Cr-tolerant, hyperaccumulator plants are exploited for their bioremediation property. The present review discusses Cr availability in the environment, Cr transfer to biota, toxicity issues, effect on germination and plant growth, morphological and ultrastructural aberrations, biochemical and physiological alterations, effect on metabolic processes, Cr-induced alterations at the molecular level, Cr hyperaccumulation and Cr detoxification mechanism, and the role of arbuscular mycorrhizae in Cr toxicity, in plants.

Chromium toxicity and tolerance in plants

Fly ash as a soil ameliorant for improving crop production--a review.

I. Abstract Chromium poisoning among leather tanners has long been known. The workers have been found to suffer from ulcers, allergic dermatitis, lung cancer, and liver necrosis due to prolonged contact with chromium salts. One of the highly catastrophic incidences of lung cancer as a result of inhaling dust containing Cr (VI) was reported in 1960 from the Kiryama factory of the Nippon-Denko concern on the island of Hokkaido, Japan. Pollution of water resources, both surface and underground, by indiscriminate discharge of spent wastes of chromium-based industries has become a serious global concern, for it has created an acute scarcity of safe drinking water in many countries. In August 1975 it was observed that underground drinking water in Tokyo near the chromium (VI))–containing spoil heaps contained more than 2000 times the permissible limit of chromium. In Ludhiana and Chennai, India, chromium levels in underground water have been recorded at more than 12 mg/L and 550–1500 ppm/L, respectively.

https://bioone.org/journals/The-Botanical-Review/volume-70/issue-3/0006-8101(2004)070[0313:CAATIA]2.0.CO;2/Chromium-Accumulation-and-Toxicity-in-Aquatic-Vascular-Plants/10.1663/0006-8101(2004)070[0313:CAATIA]2.0.CO;2.pdf

Kamla Kulshreshtha

Papers

Chromium Accumulation and Toxicity in Aquatic Vascular Plants

Do leaf surface characters play a role in plant resistance to auto exhaust pollution

Seasonal dynamics of methane emission from wetlands

Impact of fly ash soil amendment on seed germination, seedling growth and metal composition of Vicia faba L.

Dust loadings on some common plants near lucknow city