Study: Groundwater contaminant perchlorate retards development of young minnows

Fathead minnows exposed to environmentally relevant levels of ammonium perchlorate in the earliest stages of life showed retarded development compared with control fish, according to a study published in the April 2005 issue of the peer-reviewed journal Environmental Health Perspectives. The fish, which were exposed to the chemical for the first 28 days of development after fertilization, had poorly developed scales, poor pigmentation, and altered thyroid hormone levels, and were significantly lower in weight and length than unexposed minnows.

Ammonium perchlorate is the primary ingredient of the solid propellant in rockets and missiles. Perchlorate salts are also used in smaller amounts in air bag inflators, road flares, and fireworks, and in the making of leather, fabrics, and paints. Discharge from rocket fuel manufacturing plants, the decommissioning of missiles, and the refueling of rockets are believed to be responsible for most of the ammonium perchlorate released into the environment.

In recent years, there has been increased concern about the presence of perchlorate in drinking water. Perchlorate has been shown to inhibit synthesis of thyroid hormones in mammals. However, relatively little research has been performed on the impact of perchlorate exposure on fish.

Scientists exposed fathead minnow embryos to water with concentrations of 1, 10 and 100 milligrams per liter (mg/L) ammonium perchlorate, levels that can occur in the environment. The exposed minnows hatched normally, but continued exposure to 10 and 100 mg/L ammonium perchlorate resulted in developmental retardation. These fish had minimal appearance of scales, and their viscera were still visible through their skin. According to the authors, this indicated that "the larval to juvenile transition in these fish had not been completed within the 28-day study period, whereas control fish successfully completed this transition."

The exposed fish were also significantly lighter-weight and shorter than control fish, and had altered whole-body levels of the thyroid hormones T3 and T4. Thyroid hormones are well known to play an important role in larval metamorphosis in certain other types of fish, the authors wrote, although the role played in minnow development is less certain. The authors noted a need to study the fish over a longer period time to understand longer-term impacts of exposure.

Dr. Jim Burkhart, science editor for EHP, said, "The potential environmental impacts of perchlorate currently are being widely studied. This research contributes to a more complete understanding of potential impacts on fish and other marine life."

The article is available free of charge at

This article originally appeared in the 03/01/2005 issue of Environmental Protection.

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