Elemental Woe

Introduction

Studies indicate an urgent need to map areas that have selenium-rich soil because the element has been linked to aridity there. A study published in the September issue of Journal of Environmental Management revealed that food grains from some arid regions in Northern India had high selenium.

For the study, researchers from the National University of Singapore and Maharshi Dayanand University in Haryana collected food grains from Rajasthan, Punjab, Himachal Pradesh and Haryana and tested the selenium content in them. They found that while extremely dry areas like Rajasthan and southern parts of Haryana had relatively higher selenium in food grains, the amount in Punjab, Himachal Pradesh and northern parts of Haryana was normal and grains from areas that were affected by floods along the Yamuna had lower levels of selenium. Estimations of selenium levels in food grains and soil showed that while the problem is intense in some pockets of Punjab and Haryana, in most parts of northern India, it is within safe limits. According to the study, the highest level of selenium detected was 0.272 mg/kg in wheat from Jind in south Haryana.

These levels are lower than those found by K S Dhillon, retired professor of Punjab Agricultural University, who has studied selenium content in soil in Punjab for about three decades. He detected up to 4.5 mg/kg of selenium in soil in some villages. Soil samples containing more than 0.5 mg/kg selenium lead to plants with more than 5 mg/kg selenium, he says. Plants containing more than 5 mg/kg are considered toxic.

Dhillon says, "In well irrigated or high rainfall areas, selenium being water soluble either leaches down to lower layers or gets transported to low lying areas. This leaching cannot take place in arid regions and selenium accumulates in the surface layer." In plants, selenium toxicity hampers root development and chlorophyll formation, while in human beings, it causes hair loss, tooth decay, nail malformation, dermatitis and neurological problems.

Another study published in the Journal of Plant Nutrition and Soil Science in April this year said that significant amount of the element could be lost from the soil during irrigation and rainfall. Dhillon, who is one of the authors of this study, said irrigation with selenium-contaminated groundwater increased selenium content of the topsoil in some pockets of Punjab and Haryana and hence the soil exhibited selenium toxicity.

His study found that selenium content of wheat shoots grown after rice cultivation (in selenium-rich groundwater) was 20 times higher than that of the maize crop, which was grown after wheat. He said that there was a negative relationship between rainfall and selenium. With decreasing rainfall, seleniferous soil is likely to have even less runoff of selenium and hence more selenium will remain in the soil. But there is still no evidence that intensity of the problem in selenium toxic areas will increase with decrease of rainfall. He stressed it is imperative to probe the link further.

Source

Down To Earth, October 2008