Commercial cultivation and heavy metal induced soil pollution
Soil is a complex substance that remains productive only if it is cared for and nurtured. Combating and addressing soil pollution is the only way to minimize the risks for food security, human health and the environment. The major part of Bangladesh is on the delta formed by the three major rivers like Brahmaputra, Ganges and Meghna.
The Ganges, Brahmaputra, Meghna river system drains a basin of some 1.76 million sq km. Over millennia the sediments have built a broad delta forming most of the area of Bangladesh and the submerged delta-plain in the Bay of Bengal. These huge sediments are the major sources of formation of 80 per cent soils of the country. The remaining 20 per cent of soils have been formed in tertiary and quaternary sediments of hills (12 per cent) and in uplifted Pleistocene terrace (8 per cent).
Nowadays, how "development would be eco-friendly of agriculture friendly" is a conflicting question under the era of neo-liberalism. Commercial cultivation has been resulted the alteration of climate as the indiscriminate use of land changes the ecosystem stability. Commercialization of agriculture and agricultural land intensifies transfer of agricultural land and water body to non-agriculture uses. Loss of agricultural land and water bodies are a common figure in this regard. Tobacco is an economic crop in Bangladesh which is fundamentally grown particularly in Chittagong Hill and Northern regions of Bangladesh.
In point of fact it is a non-food plant harmful for health, environment and society. Consequently, its fabrication raises ethical concerns. In Bangladesh, major farmers have no ethical and environmental concerns about tobacco production. Tobacco yield owns that the variables fertilizers, pesticides, seed, labours, support from the company and land quality is positively significant to affect the tobacco yield.
However, heavy metals, one of such toxic contaminants, are not bio- and thermo-degradable, hence accumulate in the environment up to hazardous levels. The soil is one of the fundamental resources in the world. For some years, reports have told of its alarming degradation by several means. If the current rates of loss are continuing then the topsoil reserves would disappear in about 150 years. Trace elements can be mobilized from arid soils through plant uptake and erosion/leaching processes, but these soils usually contain higher contents of trace elements than other soils.
Soil Cadmium is derived from weathering of rocks and minerals or from numerous anthropogenic sources. Two primary sources of heavy metals in the soil are (i) the natural background i.e. metals derived from parent rocks; and (ii) the anthropogenic contamination i.e. those originated from human activities. Most of the soil metals today have originated from anthropogenic sources than natural ones. Meanwhile, irrigation of agricultural soil with polluted municipal and industrial wastewater is another vital source of pollution.
Heavy metal content is one of the deciding factors for the quality of phosphate fertilizers, which does not have any standard permissible limit because the maximum allowable content depends on soil characteristics, irrigation water quality, crop type, etc. Fertilizers are one of the key factors for agricultural development to promote food security and maintain the agricultural productivity of soils. It also causes serious environmental contamination notably in the agricultural soils. Day by day fertilizer unfortunately now has becomes a 'necessary evil'.
Excessive and continuous uses of nitrogen and phosphorous fertilizers for decades have converted the agricultural soils into virtual chemical time bombs. However, soil is polluted by pesticides and organic and mineral fertilizers.
To ensure food quality, the heavy metal contamination of food is one of the most important assessment parameters. In agricultural field, heavy metal contamination is an important problem that directly posing a serious health risk for human beings and animals. In the world, especially in Latin America, the East, and South Asia, the Middle East and the West Indies rice is one of the most important staple foods which are the staff of life for 3 billion people. It also provides about 30 per cent of the dietary energy and 20 per cent of the dietary protein in Asia. However, rice may contain significant amounts of contaminants such as arsenic (As), cadmium (Cd) and lead (Pb).
Every year, 5th December celebrates as world soil day to aware the mass people about soil pollution, soil biodiversity, soil health and related climatic insurgencies. This year (2018), the issue of world soil day is "Be the Solution of Soil Pollution''. In our country, heavy metal related pollution is augmenting day by day where soil profile, soil texture, soil structure, soil nutrients are fractured which is inimical for crop production and soil ecological health. Global context of climatic insurgencies demand sustainable solution of heavy metal, particularly cadmium pollution.
Shishir Reza is an Environmental Analyst, Bangladesh Economic Association & Reyad Hossain is Graduate in Environmental Science, MBSTU