Soil microbial responses to reclaimed water irrigation and implications for soil health

Reclaimed water (RW), which is treated municipal wastewater suitable for beneficial reuse, is increasingly recognized as a viable option for agricultural irrigation worldwide due to its numerous benefits. However, RW contains various contaminants whose fate in soils is variable and not fully understood. These contaminants may accumulate in soils, degrade, be taken up by plants and microbes, leach into groundwater, or be transported to surface waters via runoff. This review examines the impacts of RW contaminants on soil microbial communities, which play critical roles in nutrient mineralization, cycling, enzyme activities, and overall soil function. Evidence from literature is mixed: some studies report reductions in total bacterial and archaeal populations and decreased diversity of arbuscular mycorrhizal fungi, whereas others indicate enhanced microbial proliferation and enzyme activity due to increased availability of microbial growth substrates. These variable effects suggest that the impact of RW contaminants on soil microbial communities and their functions depends on soil properties (e.g., pH, organic matter content, texture, and mineralogy), the type and concentration of contaminants, and the wastewater treatment methods applied. Further research across diverse soil types and environmental conditions is needed to better understand how RW contaminants influence microbial communities, enzyme activities, and overall soil health.