Assessment of Plastic Fractions and Selected Heavy Metals in Groundwater and Wastewater Used for Irrigation Practices in Peri-Urban Areas of Okara City, Pakistan

Abstract

Background: Fresh water and groundwater scarcity is one of the major concern around the globe. Pakistan is also facing major water crisis which has highlighted the country as a water stressed nation. Pakistan earns a major portion, (21%), of its GDP from agriculture. Therefore irrigation water is one of the most water demanding sector. Due to unavailability of groundwateron such a large scale, farmers have shifted toward wastewater irrigation. Other than the fact that wastewater is rich in organic matter and nutrients, many harmful elements such as heavy metals, pathogens, plastic fraction etc. are also a part of its chemistry. They can cause significant environmental concerns such as polluting soil and groundwater table and health concerns for people consuming the agricultural products grown is wastewater. Objective: District Okara is one of the major agricultural districts of Punjab, Pakistan. This area is famous for fertile lands and good agricultural yield. Along with groundwater and canal water irrigation, wastewater irrigation is one of the major irrigation source in the district. The objective of this study was to observe the quality of wastewater and groundwater used for irrigation by evaluating their physiochemical properties and quantifying the concentrations of heavy metal and plastic fractions (macro- and micro-plastics), as their concentrations can impact the quality of food produced in the soil irrigated using these water systems. Basic quantification and characterization of plastic fraction is also an objective of this study since plastic pollution is of serious concern as an emerging pollutant around the globe. Health risk assessment of waste was also conducted in order to determine whether or not the selected groundwater wells are safe for human consumption. Methodology: The study design was based on two north wastewater disposal stations and a south wastewater sewage line, which provide wastewater to agricultural fields of northern and southern parts of the city and 11 groundwater wells distributed at random locations in the peri-urban and rural areas of Okara were selected. Samples were collected, the on-field physiochemical parameter were recorded and the samples were preserved accordingly. All the key points of quality control and quality assurance were kept in check throughout the study. Heavy metals analysis were performed on the wastewater and groundwater samples using atomic absorption spectrometry and then the data was evaluated based on different statistical analysis. Plastic fractions were segregated and then visually identified and recorded. MPs were identified and enumerated using a compound VI microscope equipped with digital camera. Health risk assessment of groundwater was performed using the standardized procedure. Results and conclusions: Heavy metal analysis of urban wastewater samples revealed that the concentrations of Cd, Zn and Cu were higher than the acceptable FAO limits for irrigation at most wastewater site. 8 out of 11 groundwater samples showed high concentration of Cd ranges between 0.01-0.02 mg/L. Health risk assessment of the selected groundwater sites revealed the risk of Cd exposure in both adults and children upon consumption, however children were relatively more prone to long term health effects by Cd exposure than adults. The quantification of plastic fractions in urban wastewater and groundwater (25±6 and 413±2828 particles/L), with fiber as the most abundant particle shape and red was the most abundant color pigment in both wastewater and groundwater samples. The size of plastic particle had an inverse relation with particle abundance, which means more particles were present in the smaller size class and vice versa. Most plastic fractions were observed in the size range of 100μm-1mm for both groundwater and wastewater samples i.e. 212 and 239 particles/L.