Assessment of Multidrug Resistant Bacterial Isolates and Heavy Metal Accumulation in Leafy Vegetables Irrigated with Domestic Sewage Wastewater

Abstract

Wastewater use in agriculture is widely practiced worldwide due to factors such as increasing water scarcity and limited access to freshwater resources. As the sources of freshwater become scarcer globally, the use of sewage water becomes an attractive and economical option for conserving water supplies. In urban areas of the world where the infrastructure for the treatment of wastewater is either unavailable or too expensive, farmers often utilized untreated sewage water as an irrigation source. This practice wastewater irrigation presents significant health and environmental challenges, including heavy metal contamination and the spread of multi-drug resistant (MDR) bacteria. The study examined the consequences of using sewage water for irrigation on the growth, heavy metal accumulation, and microbiological safety of the studied vegetables which are often consumed raw such as Coriandrum sativum (coriander), Raphanus sativus (radish), and Lactuca sativa (lettuce). The results revealed that using untreated sewage water for irrigation increased the growth of vegetables by 20–30% relative to the control but the heavy metal concentrations detected in the edible portions exceeded the FAO/WHO standard limits. Moreover, 100% of bacterial strains isolated from vegetables irrigated with untreated sewage water were identified as MDR, with 46% isolates forming strong biofilms, posing serious public health risks. Treated sewage water maintained the growth of vegetables comparable to the control and reduced accumulation of toxic heavy metals in vegetables as well as microbial hazards posed to humans by 40%, highlighting its potential as a safer alternative for agricultural irrigation. Conversely, autoclaved sewage water eliminated microbial activity, but the growth of the studied vegetables decreased significantly, emphasizing the essential role of microbial interactions in the development of plants. In summary, this study underscores the dual impact of irrigation with sewage water, promoting the growth of crops while introducing significant environmental and health risks. It highlights the urgent need for effective wastewater treatment processes to mitigate heavy metal contamination and MDR bacteria dissemination, ensuring the safety of agricultural products.