Chemical contamination occurs when food comes into contact with chemicals – and can cause ‘chemical food poisoning’. Some of the most common causes of chemical contamination are cleaning products, or unwashed fruits and vegetables.Other sources may include food containers made from non-safe plastics, pest control products or some chemicals used in food processing.ome of the most common causes of chemical contamination are cleaning products, or unwashed fruits and vegetables. Other sources may include food containers made from non-safe plastics, pest control products or some chemicals used in food processing.