Plastic mulch and pesticides residues effects on the lettuce growth

Plastic mulch and pesticide residues are ubiquitous contaminants in agricultural soils. In the field, pesticide residues remain in the soil for months and can accumulate over time. However, most studies investigating the effects of these contaminants use pristine chemicals and test them in lab conditions. We tested 3 plastic mulches and 3 pesticides commonly used by farmers. Low-density polyethylene (LDPE), Pro-oxidant Additive Containing plastic (PAC) and biodegradable plastic (BIO) mulches were laid in a field for 4 months, shredded into micro- and macro-sized plastic pieces and then added to a mesocosm soil experiment along with the pesticides. Plastics and pesticides were left in the mesocosm to incubate for a year in field conditions before lettuce seedlings, Lactuca sativa, were planted. After a 14 week growing period, we measured the basal diameter, number of leaves, leaf area, fresh shoot biomass, dry shoot biomass and shoot water content. We observed decreased leaf area, fresh shoot biomass and dry shoot biomass in plants growing in soil where BIO plastic was present as compared to the control treatments. These results follow previous studies and call for a more detailed testing procedure before BIO mulches are approved for agricultural use and made available on the market.