Monitoring pesticides in post-consumer containers by GC/TOFMS and HPLC/DAD after the triple rinse method

Plant protection products are commercially available both in solid form and liquid formulation solutions. In Portugal, the volume of pesticides sold in 2019 translates into almost 800 tons of packaging material. Most of these materials are plastic containers, the remainder being mainly cardboard, mixed materials and metal. After use, the containers may still have relatively high amounts of toxic pesticides, which render them hazardous. The triple rinsing practice has been highly suggested to reduce the amount of pesticides in the empty containers, in order to allow further recycling. In Portugal there is an ongoing campaign to encourage the triple rinsing, aiming to make this type of waste non-hazardous. Thus, a way to monitor the concentration of leftover pesticides in the containers is necessary. This work describes the development of a methodology for the determination of 32 pesticides in used containers, and a monitoring campaign carried out between April 2018 and February 2021. The method involves grinding the material to a small particle size (<0.5 mm), followed by ultrasound-assisted liquid extraction with a tetrahydrofuran solution and analysis by GC/TOFMS and HPLC/DAD. The recoveries obtained were between 71–116% for all compounds except captan (62%), triclopyr (40%) and mesotrione (32%). The limits of detection and quantification were between 2.6–53.6 mg/kg for GC/TOFMS and 8.1–162.5 mg/kg for HPLC/DAD. The first three collections of containers (containing several materials from plastic to metal) showed high values for the sum of all analytes (1661 to 4332 mg/kg), whereas the last five collections (only plastic materials) presented a lower content (180 to 521 mg/kg), which reflects the effectiveness of the campaign promoting the triple rinsing practice of plastic containers.