Estimation of Subsurface Pollutant Load and Its Seasonal Variation in an Irrigation Channel

Abstract

Concentrations of heavy metals in irrigation water and soil were examined to determine the level of contamination in a particular irrigation channel in Gazipur, Bangladesh. In this conduit, effluent from households, industries, and municipalities was combined with irrigation water. The study was carried out in order to estimate pollutant loads along a wastewater irrigation channel and to conceptualize seasonal changes in composite wastewaters. A total of six wastewater and nine contaminated soil samples were collected directly from the study area and analyzed for this project. From February to March, before the monsoon, the pH of the water is too low for this channel to be used for irrigation. At the end of the monsoon season, from April through May, all wastewater tests were within these parameters, making them suitable for irrigation. Considering the standard limits, Pb, Cr, and Cu concentrations in all wastewater samples were found unsuitable for irrigation and thus problematic for soils and crops. The concentration of Cd in the wastewater samples ranged from 27.82 to 88.36 mg/L, whereas the tolerance limit for Cd in irrigation water is 0.01 mg/L. In soil samples from the three places chosen, the levels of Pb were below the safe limit and the levels of Cr were above the safe limit. The heavy metal pollution index of all the sites crossed the safe limit. On the basis of the geo-accumulation index and the pollution index, Pb indicates no pollution and Cd indicates very high levels of pollution in all locations. The maximum enrichment factor was found for Cd, Pb, and Cu, which have minor enrichment, Ni, which has no enrichment, and Cr, which has moderate enrichment. The study also tried to link heavy metals in wastewater to their deposition in soil and seasonal and temporal variations. The study revealed that industrial effluent utilized for irrigation was closely related to the accumulation of heavy metals in soils. Since irrigated agricultural soils are likely to be exposed to harmful wastes, it is crucial that the effluents from the industrial region of Gazipur are appropriately controlled.