Study suggests continuous monitoring of the water and soil quality in wastewater irrigated areas in Musi basin

The large volume of wastewater remains untreated due to inadequate wastewater treatment facilities and the struggle to regulate it in many countries in the world. But it is being reused as a source of irrigation in urban and peri-urban areas. In many parts of the world, for example, Australia, the United States of America, China, and a few European cities have included wastewater reuse as an important dimension of water resource planning and management. In India, around 80% of all wastewater produced is untreated and discharged onto soils and surface water bodies, and thus leached into the groundwater system.

However, the proper planning and reuse of domestic wastewater for agriculture and other sectors alleviates water pollution, conserves freshwater resources, increases food production, and reduces fertilizer costs. Yet, there are not many studies available that explain wastewater irrigation impacts on the total water circulatory system from soils to water to crops.

The present study ‘Impact of urban wastewater reuse for irrigation on hydro-agro-ecological systems and human health risks: A case study from Musi River basin, South India’ by Shivarajappa et al is an attempt to assess the impact of wastewater use on soil, crop, and water and associated health risks based on exposure risk model. 

The farmers in the urban and peri-urban areas practice wastewater irrigation. The major crops grown in the area are paddy, para grass, and vegetables. The present study covered four major villages Gowrelly, Thimmaiahguda, Quitbullapur, and Pasumamula covering 100 acres where wastewater is being used for irrigation since 1991.

The river Musi is polluted due to municipal sewage and industrial wastewater that contains high concentrations of nitrogen, phosphorus, and metals such as lead, zinc, and iron. The study focused on the presence of various contaminants (heavy metals) in wastewater circulatory transport systems including surface and groundwater as well as in soil and crops that are irrigated in wastewater agricultural areas situated in the surrounding Musi River to know the extent of pollution.

The study analysed physical (pH, electrical conductivity - EC, turbidity, oil and grease, total suspended solids - TSS), chemical (Zn, Cr, Pb, Mn, Cu and Ni) and biological (biological oxygen demand - BOD, chemical oxygen demand - COD, dissolved oxygen - DO) parameters.

Furthermore, the human health risk assessment model was used to assess the potential of non-carcinogenic and carcinogenic health risks of heavy metals for infants, teens, children, and adults (male and female) via different exposure pathways in agricultural soils, water, and crops prescribed by the United States Environmental Protection Agency (US EPA).

The salt content in soils and water is gradually increasing which may create waterlogging and damage to soil structure which can negatively impact agricultural production and its sustainability in the future. Water quality is among the most important environmental challenges related to sustainable development and agriculture, particularly in countries where agriculture is the backbone of the economy. Severe metals and other toxic contaminants endanger water, soil, and agriculture. Once a carcinogenic component reaches the food chain, it is extremely difficult to eliminate and has a devastating carcinogenic impact on humans.

The hazard index and total cancer risk were evaluated from different waters for 4 years for different age groups that are infants, children, teens, males and females. The exposure of heavy metals to human health is proportional to their daily consumption. This study, however, considered consumption through drinking water and dermal adsorption. The human health risk assessment based on heavy metals revealed lower to moderate health risks.

The chloride, magnesium, calcium, sodium, potassium, and phosphorus are within permissible ranges of the Indian Soil Standards. The measured organic carbon (OC) content in the soil samples during the study period ranges from 4100 mg/kg to 12,900 mg/kg. The permissible value of organic carbon (OC) ranges between 5000 mg/kg and 7500 mg/kg. The OC values in 2020 were within the allowable limit of Indian soil standards, remaining all the years the OC values exceeded the permissible limit of Indian soil standards.

In an overview, the study results indicated the increasing trend of salinity in groundwater, traces of heavy metals in soils and water, exceeding concentrations of nitrate (NO3) and biological contamination. However, the study suggests continuous monitoring of the water and soil quality in wastewater irrigated areas to take remedial actions for sustainable agriculture development and protect ecosystems. The mapping of the subsurface and modelling of solute transport to understand groundwater and associated contamination transport will be attempted in future studies.

Hence, there should be a centralized mechanism for treating domestic and industrial sewage before using it for irrigation. Natural treatment method such as artificial/natural wetlands and reed beds can be used for the removal of contaminants from sewage. The decentralized and operational sewage treatment plants can also be planned for the whole Musi River basin to avoid untreated wastewater disposal to streams and the river course.