What happens if the containers are used to store noxious chemicals before returning to be refilled? Will PET absorb chemicals?

Storage of garden chemicals like weedkillers, pesticides, or fuel oils and retention of harmful contaminants during subsequent washing and cleaning processes is a potential problem as absorption could occur.

The very strict inspection procedures in washing and cleaning plants are designed to detect and eliminate any suspect bottles.  Optical detectors and sophisticated electronic 'sniffers', in addition to manual inspection, ensure that these bottles are eliminated; such devices are used before and after washing.  Contaminated bottles are not known to have passed through the extremely rigorous inspection systems.