Artificial Progestins In Women's Drugs Affect Fish Reproduction

July 30, 2009

Release from: Environmental Health News

This study reports for the first time that progestins, which are used in combination with other hormones in birth control pills and hormone replacement therapies, decrease egg production in fish.

Fish produced fewer – or no eggs at all – after only one to two weeks of exposure to either of two different types of synthetic progestin hormones found in women's reproductive drugs. The more potent of the pair of progestins also lowered sperm production and affected behavior in male fish.

This is the first study to show that a progestin used in human pharmaceuticals can affect fish reproduction at environmentally-relevant levels. Women's contraceptives and menopausal drugs contain the progestins.

Progestins are synthetic versions of the natural hormones progestogens (or gestagens, of which progesterone is an example). Progestogens help regulate the menstrual cycle and are involved in maintaining pregnancy.

Progestins can be combined with estrogen in birth control and hormone replacement therapy drugs. Alone, they act as a “mini-pill” to stop the release of eggs from the ovary and to reduce the risk of cervical cancer in menopausal women. Several different forms of progestins are used in these medications, and they vary in their potency.

Women taking the birth control pill or hormone replacement therapies excrete progestins in their urine. Though few studies have looked for progestins in municipal wastewaters, one type used in the study – levonorgestrel – was found at low levels in sewage effluents (15 parts per trillion) and surface waters (1 part per trillion). Just like the estrogen hormones that have received a lot of recent attention, fish living downstream of these discharges are likely exposed to progestins.

In this study, a common fish species, the fathead minnow, was exposed to two different progestins: the most heavily prescribed progestin in the birth control pill (levonorgestrel) as well as a newer form used in contraception, drospirenone. Fish were exposed to 0.8, 3.3 and 29.6 parts per trillion (nanograms per liter) of levonorgestrel or 0.66, 6.5 and 70 parts per billion (micrograms per liter) of drospirenone for 21 days (4 tanks per treatment with one pair of fish per tank). Total numbers of eggs, numbers of eggs per clutch, spawning behavior, coloration of the fish (a secondary sexual characteristic controlled by hormones), and egg and sperm development in the ovaries and testes were monitored and compared to fish in control tanks.

Reproduction in the fish was affected after only one week of levonorgestrol exposure. Female fish exposed to the artificial hormone produced fewer eggs (3-fold fewer than controls) at all exposure levels, had more eggs that failed to mature and became masculinized at the higher concentrations. Male fish produced fewer sperm, became less aggressive and were less interested in spawning. After two weeks, egg production stopped in all of the exposure tanks.

The lowest concentrations of this progestin are likely to be found in rivers downstream of wastewater discharges.

The other progestin, drospirenone, was much less potent, affecting fish reproduction after two weeks. Concentrations 8,000 times higher (6.5 micrograms per liter) than the levonorgestrel treatments stopped egg production and any breeding in the fathead minnow. However these levels would not likely be found in the environment based on known use and dilution in river waters.

These results of the study are not surprising because fish – like people – produce progestogens that are important for reproduction. In fish, the hormones play a crucial role in helping eggs to mature.

Given their widespread use in pharmaceuticals and likely presence in the environment, progestins should be considered as another class of hormones with the potential to impact the health of wild fish.