Recently, the U.S. Food and Drug Administration has been planning to review the recommendations that pregnant women and young children limit their consumption of fish to avoid exposure to potentially harmful amounts of mercury.

According to a draft report from the agency, the health benefits of eating fish appear to outweigh the potential dangerous effects of mercury. As a response, the Environmental Protection Agency has released a memo to the White House calling the 270-page FDA study “scientifically flawed and inadequate” and an “oversimplification” which lacks analytical rigor.

Fish are the main sources of human exposure to mercury. High levels of mercury in the blood stream can harm the nervous system of fetuses and young children and can cause learning disabilities. Prenatal and infant mercury exposure can cause mental retardation, cerebral palsy, deafness and blindness. Experts say that fish and shellfish have a natural tendency to concentrate mercury in their bodies in the form of methylmercury, a toxic organic compound of mercury. Shark, swordfish, king mackerel, albacore tuna and tilefish contain a higher concentration of mercury than others. The FDA characterizes shrimp, catfish, pollock, salmon, and canned light tuna as low-mercury seafood.

The FDA and the EPA have recommended that women of child-bearing age and young children not eat species of fish that are high on the food chain such as shark, swordfish, king mackerel or tilefish.

According to the Centers for Disease Control and Prevention, about 8 percent of U.S. women of childbearing age have enough mercury in their blood to be at risk of having babies with learning disabilities.