1. Contract relationship between the courier company and the sender: the sender gives the goods to the courier company, and the courier company promises to deliver the goods to the designated place within a certain period of time.

2. The contractual relationship between the courier company and the consignee: the consignee receives the goods through the courier company, and the courier company has the obligation to ensure that the goods are not damaged or polluted during transportation.

3. Tort between the courier company and the chemical plant: the dangerous goods produced by the chemical plant leaked during transportation, resulting in the pollution of the courier items, causing personal injury and property losses.

4. Tort between the sender and the chemical plant: the sender did not inform the courier company that the goods contained dangerous goods when sending the goods, which led to the courier company not taking corresponding safety measures during transportation, resulting in personal injury and property loss.