The reference in the link is fairly lengthy. If you go beyond the first paragraph there sections: Disease and parasites, Pollution and contaminants... (about 10 more sections). However under Pollution and contaminants there are some eyebrow raising bits of information. "In sites without adequate currents, heavy metals can accumulate on the benthos (seafloor) near the salmon farms, particularly copper and zinc.[14]

Contaminants are commonly found in the flesh of farmed and wild salmon..."