Irrigation Water Quality for Leafy Crops: A Perspective of Risks and Potential Solutions

Abstract

There is increasing evidence of the contribution of irrigation water in the contamination of produce leading to subsequent outbreaks of foodborne illness. This is a particular risk in the production of leafy vegetables that will be eaten raw without cooking. Retailers selling leafy vegetables are increasingly targeting zero-risk production systems and the associated requirements for irrigation water quality have become more stringent in regulations and quality assurance schemes (QAS) followed by growers. Growers can identify water sources that are contaminated with potential pathogens through a monitoring regime and only use water free of pathogens, but the low prevalence of pathogens makes the use of faecal indicators, particularly E. coli, a more practical approach. Where growers have to utilise water sources of moderate quality, they can reduce the risk of contamination of the edible portion of the crop (i.e., the leaves) by treating irrigation water before use through physical or chemical disinfection systems, or avoid contact between the leaves and irrigation water through the use of drip or furrow irrigation, or the use of hydroponic growing systems. This study gives an overview of the main problems in the production of leafy vegetables associated with irrigation water, including microbial risk and difficulties in water monitoring, compliance with evolving regulations and quality standards, and summarises the current alternatives available for growers to reduce microbial risks.

Keywords: GAP; QAS; food safety; hydroponics; irrigation water; leafy vegetables; water disinfection treatment.

Figure 1

A secondary treatment wastewater plant located in a greenhouse production unit to provide irrigation water for tomato production. Reprinted with permission of Quality and Safety Lab CEBAS-CSIC.

Figure 2

UV-C treatment system where water passes through a vessel while it is illuminated by UV-C lamps located in the vessel. Reprinted with permission of Quality and Safety Lab CEBAS-CSIC.

Figure 3

Nutrient film techniques (NFT), a type of soilless systems where a thin film of nutrient solution flows through plastic channels which contain the plant roots and laid on a slope in order to grant the constant flow of nutrient solution. Source: James M. Monaghan (Harper Adams University).