All of the following are common causes of chemical contamination except for:

The presence of improperly canned food is not typically categorized as a common cause of chemical contamination. Chemical contamination often arises from substances that can directly introduce harmful chemicals into food, like poorly labeled cleaning agents or cleaning supplies that have not been stored appropriately.

For example, improperly labeled cleaning supplies can easily lead to their misuse, resulting in chemical residues that contaminate food. Similarly, improperly cleaned produce can carry residues from pesticides or chemicals used during its growth or processing. Improper food storage can contribute to chemical leaching from containers or packaging materials into food.

In contrast, improperly canned food usually relates more to physical contamination or spoilage related to process failures, such as inadequate sealing or high acidity in the food creating a breeding ground for bacteria. Thus, while all other options are directly linked to chemicals that may pose health risks through ingestion, improperly canned food does not fit into the realm of chemical contamination in the same way.