Humans have been adding toxic chemicals to the air, land and water for centuries, and it’s caught up with us—and our fisheries. Unfortunately, as bad as things are, we could only be seeing a glimpse of how toxic our aquatic habitats have become and how we continue to make a bad situation worse.
History Of Poison
Most chemicals are toxic—it’s just a matter of concentration and exposure. The list of such chemicals continues to grow thanks to industrial chemists who create new materials, analytical chemists who’ve improved our abilities to detect contaminants, and toxicologists who keep finding new effects.
When contamination problems were forcefully addressed by the Clean Water Act in 1972, toxins were thought of more narrowly as chemicals that killed plants or animals outright (what toxicologists refer to as “acute lethal toxicity”), or caused macroscopic effects such as deformities, wounds or aberrant behavior. By the 1980s, water-quality criteria had been developed for about 150 chemicals, and lethal concentrations of more than 270 chemicals had been established for fish and other aquatics.
Gargantuan efforts were initiated to fix the situation. Especially nasty and persistent chemicals, such as organochlorines like DDT and polychlorinated biphenyls (PCBs) were banned, water laws set permissible discharge levels for other chemicals, and remediation efforts attempted to clean up hotspots.
However, it soon became apparent that many chemicals also had sublethal and less readily apparent effects on fish and other aquatic life. We had only been dealing with the tip of the iceberg.
Suspecting that contaminants were present in the environment at or below detection limits and that additional unidentified chemicals may be contributing to problems, environmental toxicologists began relying on “biomarkers” in aquatic organisms to monitor pollutants. Biomarkers include anatomical variation (such as unusual organ size), visible sores, microscopic anomalies (such as changes in tissues), and chemical compounds in tissues and body fluids that function like hormones. These indicate exposure to contaminants at very low levels, and chemicals with sublethal effects.
Most current biomarker monitoring in fisheries is focused on hormones and what are known as endocrine functions. Hormones are chemicals produced or released by one body organ that affect the function of one or more other organs. The network that regulates bodily functions via hormones is the endocrine system. It plays a critical role in normal growth, development, behavior and reproduction.
That said, even small disturbances in endocrine function may have profound effects. Unfortunately, manmade chemicals have proved all too capable in this regard, mimicking natural hormones and interfering with the proper functioning of the system. This is especially true for fish in highly sensitive early development periods.
More troubling is that small changes in endocrine status may have consequences that don’t become evident until much later in life or even subsequent generations.
How Is This Happening?
Toxic chemicals come from everywhere, and directly or indirectly, through all of us. Industry releases them through regulated and unregulated discharges. Agriculture intentionally applies known toxins to maximize food production for a growing human population. Mines are a direct source of lead, mercury, selenium and zinc. Combustion of coal and incineration of wastes pumps mercury into the atmosphere and ultimately the water.
Concentrated animal feeding operations (CAFOs) are a source of natural and synthetic hormones, as are people. Many pharmaceuticals (such as birth-control pills) pass wastewater treatment plants unaltered. Whether administered to animals or humans, many of these chemicals disrupt endocrine function in fish.
Contaminants can affect any level of the aquatic food web, from phytoplankton to fish, and the aquatic community can be jeopardized when key links in the food chain are broken. A herbicide or antibiotic that kills phytoplankton will trigger declines in zooplankton. A chemical that poisons zooplankton can reduce larval fish survival. And so on.
As toxicologists forge ahead with studies of endocrine disruption and other sublethal effects in fish, similar effects remain unstudied among the many species that comprise the lower, but essential, levels in the food web. It is certain that contaminants used in the past, present and future will have significant effects on fish and aquatic ecosystems.
Solutions to these problems will target not only industry and agriculture, but must also focus on an ironically health-conscious and chemically-dependent populace. Simply put, there are too many people, and we’re adding more contaminants to the water than can be processed by normal physical, chemical and biological processes.
Technology deeply rooted in basic ecology and biodiversity may partly come to the rescue, although not without our concerted effort to stop contamination in the first place. It’s called “bioremediation,” which means using microorganisms (bacteria and fungi) to degrade, assimilate, metabolize or detoxify unwanted chemicals.
For example, Dr. Hamid Borazjani at Mississippi State’s Forest Products Laboratory has isolated bacteria that can degrade toxic accumulations of creosote and pentachlorophenol at wood-processing sites.
Phytoremediation uses plants instead of microbes to rid soil and water of contaminants. At Colorado State University, Dr. James Linden and students have found that water lettuce and native water milfoil break down antibiotics tetracycline and oxytetracycline, which are extensively used in CAFOs.
The remediation capabilities of a world full of plants, bacterial, and fungi is just beginning to be explored. In the meantime, the fish would appreciate your help in reducing contaminant inputs.