Diphenyls are a potential threat to the environment. How are these produced from aryl halides?

In environmental conditions diphenyl is formed during the incomplete combustion of mineral oil and coal and it is also present in the exhaust gases of vehicles and in exhaust air from residential and industrial heating devices. The kidneys of animals are also poisoned due to the ingestion of biphenyls. In rats, fetotoxicity has been occurring if they are exposed to high levels of biphenyl. The preparation methodology of aryl halide involves the reaction of Chlorobenzene with sodium in dry ether give diphenyl. This reaction is known as Fittig reaction.