Hormone-like Contaminants Block Trout’s Ability to Sense Predators
There has been significant success in decreasing the levels of chemical contaminants in our nation’s water ways in recent years, thanks to the Clean Air and Water Acts passed by Congress. However, low levels of many contaminants (such as metals, pesticides, and synthetic molecules like PCBs) persist in many rivers and streams, home to salmon and related trout species.
Salmon and trout utilize a natural, chemical signaling system and are able to sniff out chemical signals in the water that may indicate food–or possibly becoming food for something else. Experiments with captive rainbow trout (conducted by Tierney, K. B., et al, published in Environmental Science and Technology, last Fall) showed that after 4 days of exposure to the contaminants (common pesticides, at comparable levels found in natural systems) the fish’s ability to smell chemical odors secreted by predators was significantly impaired. Specifically, they could not sense their distance from a nearby predator. This impairment raises the likelihood that it might, in the wild, swim directly into range of a hungry grizzly bear. Over time, this inability could have dire consequences for the fish population and its chances for long-term survival.
Though the experiments were done with Rainbow trout (and in a captive state), they are close relatives of salmon, which is an important commercial fish in several regions of the world (including this author’s home region of the Pacific Northwest). The authors believe that the potential risk would be similar for salmon and that this may be one reason for the dramatic decrease in salmon stocks in much of North America.
Previous research has shown that large, synthetic molecules (or endocrine disruptors [EDs] or endocrine disrupting chemicals [EDCs], or xenoestrogens) which resemble natural hormones, interfere with the natural reproductive cycles of fish, and can make some animals sterile. While there are a few natural contaminants, such as phytoestrogens from plants, most of these are artificial (like diethylstibestrol [DES]), and result from industrial manufacturing processes. Some of these xenoestrogens are the break down components of larger synthetic compounds (as with some industrial polymers).
Environmental educators point to this issue as instructive; it shows how industrial activity in one sector often impacts negatively industrial activity in another sector, and thus why wise management practices and strict enforcement of water quality laws is vital to both the economic and ecologic future.
For further references and research on this issue, check out these resources:
Household Products Database. National Institutes of Health.
Available: http://householdproducts.nlm.nih.gov/
PAN Pesticide Database. Pesticide Action Network.
Available: http://www.pesticideinfo.org/
photo: Eric Engbretson / US Fish & Wildlife Service
