There have been concerns about rising levels of mercury in walleye fish; a study by the Canadian Ministry of the Environment noted an "increasing concentration trend" but that concentrations were within acceptable limits established by authorities in Pennsylvania. Because of the threat of PCBs, It was recommended, that persons eat no more than one walleye meal per month. Because of these and other concerns, in 1990, the National Wildlife Federation was on the verge of having a "negative fish consumption "advisory"" for walleye and smallmouth bass, which had been the main catch of an $800 million commercial fishing industry.