Impacts of standard and ‘low environmental impact’ greywater irrigation on soil and plant nutrients and ecology

• Pot-trial comparing irrigation with standard and low environmental impact greywaters.
• Greywater irrigation impacted plant biomass and nutrient uptake.
• Low impact greywater reduced soil phosphatase and increased worm avoidance.
• Detergents marketed as low environmental impact not necessarily safe for irrigation.

Interest in recycling greywaters is increasing as population growth, pollution and climate change increase pressure on water resources. There has been little research investigating impacts of irrigating untreated greywater on soil and plant health and to our knowledge no studies comparing greywater from standard with “low environmental impact” detergents. A soil-pot trial with lettuce and radish compared tap water, nutrient solution, and grey water (standard and minimal impact) irrigation. Greywater had impacts on plant biomass and nutrition, soil enzyme activity, and worm avoidance. In particular, there was little indication that the minimal impact greywater was safer for irrigation than the standard greywater. The minimal impact greywater was the only greywater treatment to have a significant negative impact on soil phosphatase activity and worm avoidance. The results highlight the need for greater understanding of the impacts of untreated greywater in irrigating vegetable gardens and especially when manufacturers make claims about the environmental friendliness of their products.