INTRODUCTION OF INTERMITTENT SYSTEM OF IRRIGATION TO REDUCE ARSENIC CONTENT IN RICE GRAINS: A PROMISING APPROACH

Over the past three decades, occurrence of high concentrations of arsenic (As) in drinking-water has been recognized as a major public-health concern in several parts of the world and especially in Ganga Delta Plain. This has led to the appearance of pathologies associated in humans with chronic exposure to As through drinking water. In addition to drinking water, As exposure from consumption of rice can be substantial, particularly for the population on a subsistence rice diet. The present work was undertaken to study the dynamics of As in the soil under both continuously flooded (CF) and Intermittently flooded (IF) fields and As accumulation in rice grains in both irrigation systems were compared. An extensive field study was conducted for two years viz. 2013 and 2014 in Nadia district of West Bengal, India. The results showed that the arsenic concentrations in the soil were 1.2-1.5 times higher under the CF compared to IF. The mean As concentration in soil (mg/kg) were 56.06 ± 2.34 and 40.23 ± 1.87 for CF and IF respectively. Also, As showed moderate enrichment in case of IF than CF where it was significant (Enrichment Factor = 2.9 and 5.2 for IF and CF respectively). Comparing the Potential Ecological Risk Index (E^As_r) of As to estimate the extent of risk posed it was seen that although moderate risk was there in both the cases but CF showed slightly higher potential (E^As_r in IF= 51.21 and E^As_r in CF= 71.37). Remarkably, the concentration of arsenic detected in the rice grain showed a sharp decline in case of IF. The average As content in rice grains of IF was 1.14 mg kg^-1 that came close to the permissible limit (1 mg kg^-1), whereas it was 1.7 mg kg^-1 in case of CF. Therefore decreasing the Oral Daily Intake of arsenic through rice from 0.85 to 0.57 mg d^-1 in IF. The results demonstrated that the increased bioavailability of As under the continuously flooded conditions is the main reason for an enhanced As accumulation in rice grains, and growing rice alternatively can dramatically decrease the As transfer from soil to grains. Thus, it can prove to be very promising in terms of food safety and human health.