Dirty water can leave a fish pooped. Living downstream from a waste-treatment plant made fish work at least 30 percent harder to survive, a new study finds.
Graham Scott is a biologist in Canada at McMaster University in Hamilton, Ontario. He led the new study. “Wastewater treatment plants are pretty good at taking stuff we put into water and treating it before it gets into our waterways,” he notes. “But not everything we flush down the toilet or down our drains gets taken out.”
For example, these plants were not designed to remove remnants of drugs. So when people pee out compounds left over after their bodies use and then break down medicines, those drugs can be released into the environment. These include the hormones in birth-control pills, the drugs used to treat depression and medicines to lower blood pressure.
Life-sustaining chemical reactions in an animal’s body (including ours) allow it to grow, move and reproduce. These reactions, taken together, are known as the creature’s metabolism. It takes a lot of energy to power these processes. Some studies have shown that even traces of just one drug can change an aquatic animal’s metabolism. It can make their bodies work harder, even when they are supposedly at rest.
“That’s energy they burn just to stay alive,” explains Scott. That also is energy no longer available to avoid predators, to find food and to mate. Instead, the animals use that extra energy to rid their bodies of the pollutants. Such chemicals can damage their cells and tissues or reprogram how their bodies respond to the environment. So their bodies work to break down those contaminants. Then they pee the remains out.
If fish respond this way when they are exposed to just one drug, what would they do when their water held a mix of them? Scott’s team wanted to know. After all, water downstream from treatment plants tends to host low levels of many such compounds.
In fact, they now report, fish exposed to such a mix can use up to a third of their energy just to deal with those pollutants. Scott’s team shared its new findings January 18 in Environmental Science & Technology.
First they trapped fish
The researchers captured bluegills in unpolluted waters near Lake Ontario. Then they divided these fish into three groups. They caged some of them 50 meters (164 feet) downstream from a nearby water-treatment plant. They caged another group in waters 830 meters (a half mile) downstream of the plant. The last fish were caged in unpolluted local water, well away from the treatment plant.
All of these fish remained caged for three weeks during the summer. Afterward, the researchers brought the fish into their lab to measure their metabolism.
They did this by putting the fish into small clear tanks of water. Each tank held a wire probe. It was attached to an oxygen sensor. The tank’s sensor measured how fast a fish had removed oxygen from the water. Oxygen is an essential ingredient for a fish’s metabolism. So the faster a fish uses oxygen, the more energy it is burning to carry out its bodily processes.
Those that had been caged closest to the treatment plant now used the most energy. They burned 36 percent (one third) more oxygen than fish in clean water. Even fish well downstream from the plant used 30 percent more oxygen than normal.
How big a deal is that? Explains Scott: “A 30 to 36 percent increase in metabolism is probably like us going for a half-hour to an hour run.” And their bodies may have been using oxygen at that rate 24/7 in the wild.
It’s not known if all fish species would react the same way. Scott’s previous research suggests an invasive species called a round goby is different. It seemed to need less energy to rid its body of pollutants.
But for species that do respond by using lots more energy, pollution could harm them, says Paul Craig. He is a biologist at the University of Waterloo in Ontario. Less energy available to eat and avoid being eaten could well reduce their survival. And extra energy spent coping with contaminants means less energy available to find a mate or produce eggs.
“It is up to us to help reduce the types of pollutants that are found in wastewater,” Craig says. That includes, he says, “not flushing leftover medication down the toilet.” He also recommends using less polluting soaps and detergents.
biology The study of living things. The scientists who study them are known as biologists.
blood pressure The force exerted against vessel walls by blood moving through the body. Usually this pressure refers to blood moving specifically through the body’s arteries. That pressure allows blood to circulate to our heads and keeps the fluid moving so that it can deliver oxygen to all tissues. Blood pressure can vary based on physical activity and the body’s position. High blood pressure can put someone at risk for heart attacks or stroke. Low blood pressure may leave people dizzy, or faint, as the pressure becomes too low to supply enough blood to the brain.
bluegill A type of sunfish (Lepomis macrochirus) found in North American freshwaters (lakes and streams) used for food and sometimes caught for sport.
breed (noun) Animals within the same species that are so genetically similar that they produce reliable and characteristic traits. German shepherds and dachshunds, for instance, are examples of dog breeds. (verb) To produce offspring through reproduction.
cell The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall.
chemical A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
chemical reaction A process that involves the rearrangement of the molecules or structure of a substance, as opposed to a change in physical form (as from a solid to a gas).
compound (often used as a synonym for chemical) A compound is a substance formed when two or more chemical elements unite (bond) in fixed proportions. For example, water is a compound made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O.
contaminant Pollutant; a chemical, biological or other substance that is unwanted or unnatural in an environment (such as water, soil, air, the body or food). Some contaminants may be harmful in the amounts at which they occur or if they are allowed to build up in the body or environment over time.
detergent A compound derived from petroleum products, often used for cleaning. Detergents work by breaking up and surrounding dirt particles or oily substances, so that they can be washed away with water.
downstream Further on in the direction in which a stream is flowing or the path at which stream water will flow in its trek to towards the oceans.
environment The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).
environmental science The study of ecosystems to help identify environmental problems and possible solutions. Environmental science can bring together many fields including physics, chemistry, biology and oceanography to understand how ecosystems function and how humans can coexist with them in harmony. People who work in this field are known as environmental scientists.
goby A small, usually marine fish that often has a sucker on the underside.
hormone (in zoology and medicine) A chemical produced in a gland and then carried in the bloodstream to another part of the body. Hormones control many important body activities, such as growth. Hormones act by triggering or regulating chemical reactions in the body. (in botany) A chemical that serves as a signaling compound that tells cells of a plant when and how to develop, or when to grow old and die.
invasive species (also known as aliens) A species that is found living, and often thriving, in an ecosystem other than the one in which it evolved. Some invasive species were deliberately introduced to an environment, such as a prized flower, tree or shrub. Some entered an environment unintentionally, such as a fungus whose spores traveled between continents on the winds. Still others may have escaped from a controlled environment, such as an aquarium or laboratory, and begun growing in the wild. What all of these species have in common is that their populations are becoming established in a new environment, often in the absence of natural factors that would control their spread. Invasive species can be plants, animals or disease-causing pathogens. Many have the potential to cause harm to wildlife, people or to a region’s economy.
journal (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or sloppy work.
metabolism (adj. metabolic) The set of life-sustaining chemical reactions that take place inside cells and bigger structures, such as organs. These reactions enable organisms to grow, reproduce, move and otherwise respond to their environments.
oxygen A gas that makes up about 21 percent of Earth's atmosphere. All animals and many microorganisms need oxygen to fuel their growth (and metabolism).
pollutant A substance that taints something — such as the air, water, our bodies or products. Some pollutants are chemicals, such as pesticides. Others may be radiation, including excess heat or light. Even weeds and other invasive species can be considered a type of biological pollution.
population (in biology) A group of individuals from the same species that lives in the same area.
predator (adjective: predatory) A creature that preys on other animals for most or all of its food.
pressure Force applied uniformly over a surface, measured as force per unit of area.
remnant Something that is leftover — from another piece of something, from another time or even some features from an earlier species.
sensor A device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information. Scientists and engineers often rely on sensors to inform them of conditions that may change over time or that exist far from where a researcher can measure them directly. (in biology) The structure that an organism uses to sense attributes of its environment, such as heat, winds, chemicals, moisture, trauma or an attack by predators.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
technology The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.
tissue Made of cells, any of the distinct types of materials that make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues.
wastewater Any water that has been used for some purpose (such as cleaning) and no longer is clean or safe enough for use without some type of treatment. Examples include the water that goes down the kitchen sink or bathtub or water that has been used in manufacturing some product, such as a dyed fabric.
Journal: S. Du et al. Metabolic costs of exposure to wastewater eﬄuent lead to compensatory adjustments in respiratory physiology in bluegill sunﬁsh. Environmental Science & Technology. Vol. 52, January 18, 2018, p. 801. doi:10.1021/acs.est.7b03745