Hazardous effects of sewage water on the environment: Focus on heavy metals and chemical composition of soil and vegetables

Pakistan is an agricultural country having the world's largest canal irrigation system. Indus basin that covers 70 percent of irrigated area for crop production is the major source of water in the country. Owing to rapid increase in population and uncertain environmental conditions, this water is not adequate to cope with the crop water requirement and needs additional means to provide extra water for agricultural purposes. The main source of irrigation is canal and ground water but the quality of ground water is so poor for the sustainability of agriculture system. To cope with the present demand, use of municipal sewage water that consists of domestic liquid waste, as well as industrial effluents, is becoming a common practice. The present study aims to reflect the hazardous effects of sewage water on the environment, with the main focus on heavy metals and chemical composition of soil and vegetables.

Industrial effluent was collected from one ghee mill, one flour mill, three textile industries and three hosieries located in Faisalabad, an industrial city of Pakistan highly affected with water pollution. All water samples were analyzed for pH, EC, SAR and RSC. Water analysis was also carried out for various nutrients and heavy metals (K⁺¹, P²⁺, Fe²⁺, Cu²⁺, Zn²⁺, Mn²⁺, Ni²⁺ and Pb²⁺). Soil samples from various depths (0‐15, 15‐30, 30‐60, 60‐90 and 90‐120 cm) were taken to analyze for EC, pH, SAR, Na⁺¹, SO₄, K⁺¹, P²⁺, Fe²⁺, Cu²⁺, Zn²⁺, Mn²⁺, Ni²⁺ and Pb²⁺ after irrigation with canal water and sewage water. Cadmium, lead and copper concentration was determined in various vegetables grown in areas irrigated with canal water and industrial effluents to determine their final concentration in the final product ultimately affecting the human health.

Although the sewage water is a source of many nutrients, it also includes a significant amount of heavy metals like Fe²⁺, Cu²⁺, Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺ and pathogens. Extensive use of this effluent for irrigation purpose has resulted in an upsurge of such metals in soils and various crops, which ultimately resulted in clinical problems in human beings.

The present study reflects the composition of sewage water and heavy metal accumulation in soil, as well as crops. It further highlights the different potential hazards to humans due to these contaminants.