The study, to be published in the journal Science, found that farm raised salmon contained high levels of pollutants like PCBs (polychlorinated biphenyls). Dioxins and PCBs are implicated in causing cancers, hormone disruption, developmental and neurological problems.
Leiner however argues that fish oil supplements can be purer than fish and are still safe to take. It also claims that it requires all fish oil suppliers to use wild fish caught in deep water rather than farmed fish.
Consumption of fish oil supplements has grown rapidly in recent years on the back of research that associates the omega-3 fatty acids found in oily fish with reduced risk of heart disease and, increasingly, protection against certain mental disorders such as Alzheimer's.
But the recent study of more than two metric tons of North American, South American and European salmon, which showed that PCBs and other environmental toxins are present at higher levels in farm-raised salmon than in their wild counterparts, could not only impact fish sales but also pose a threat to consumption of fish-derived supplements.
Leiner Health Products says that random tests carried out by the University of Southern California School of Pharmacy (USC) on 18 different lots of fish oil supplements found no PCBs, dioxins or heavy metals such as lead, cadium, mercury or arsenic in any of the samples.
The finding "proves that people can take fish oil supplements without risking their health due to possible environmental contaminant intake", according to Dr Roger Clemens, director of Analytical Research & Services, USC School of Pharmacy.
The study follows recent media scrutiny of the US Food and Drug Administration's warnings on mercury contamination of fish stocks.
Leiner, the largest manufacturer of store brand vitamins, minerals and supplements in the US, uses molecular distillation to remove pollutants from fish oil, which traps virtually all contaminants, it claims.