Complex sentence: In the United States the FDA has an action level for methylmercury in commercial marine and freshwater fish that is 1.0 parts per million (ppm), and in Canada the limit for the total of mercury content is 0.5 ppm.
Split into simpler sentences: In the United States, the FDA has an action level for methylmercury in commercial marine and freshwater fish that is 1.0 parts per million (ppm). In Canada, the limit for the total of mercury content is 0.5 ppm.