Fish get wasted on wastewater

In most cities sewage is treated to remove most of the things that we don't want going into the environment. But, some things get through and out to sea. The Western Treatment Plant in Melbourne, which treats over 50% of Melbourne's wastewater (including my contribution), releases large amounts of nitrogen into Port Phillip Bay. Indeed, a 1996 report from the Commonwealth Scientific and Industrial Research Organisation recommended that nitrogen released from the Western Treatment Plant be reduced by 1000 tonnes per year. Nearly 20 years later they've achieved half that amount.

The Western Treatment Plant. Covering 10,500 hectares it treats about 50% of Melbourne's wastewater.

Nitrogen pollution is significant issue. It, along with other types of nutrient pollution, has been linked to coral and seagrass declines, and jellyfish blooms. Other things that cause problems in the ocean also slip through sewage treatments plants. From the relatively large things, like plastic fibers from clothing, to the very small, like the drugs we take.

Not all drugs remain active after they've done their job in the human body, but many do. One of the best known and most researched drugs to escape sewage treatment is ethinyl oestradiol, the active ingredient in birth control pills. Decades of research has shown that ethinyl oestradiol has negative impacts on fish and other aquatic organisms. Even very small doses can lead to male fish that produce eggs in their testes, leading to reduced fertility and potentially to population collapse (Kidd et al. 2007).

Sections through the testis of two male fish showing developing eggs, which are the large circular cells surrounded by purple staining tissue. The smaller purple staining flecks are the sperm cells.

Many recreational drugs also make it through wastewater treatment, such as illicit  amphetamines (Kasprzyk-Hordern et al. 2009). To my knowledge, it has not been shown that these arrive in the environment at high enough doses to cause any negative effects. Caffeine, my favorite recreational drug, is detected in seawater at concentrations high enough to produce measurable, but probably minor effects in mussels (del Rey et al. 2011, 2012).

Exposure to the concentrations of caffeine that are normally found in the environment probably have little or no effect on fish. Unlike caffeine, some drugs can build up in the body tissues of fish, making chronic exposure to even low concentrations a risk. Recently a study found that the concentration of a common anti-anxiety medication, oxazepam, was six times higher in the muscle of redfin perch (Perca fluviatilis) than it was in the surrounding river water (Brodin et al. 2013).

A redfin perch, Perca fluviatilis, in an aquarium (photo Wikipedia)

Interestingly, Brodin et al. went on to test what effects oxazepam had on the redfin perch. Annoyingly, they used concentrations of the drug that were three times higher than they recorded in the river and higher than other studies have documented. But, their treatments produced levels of the drug in the muscle tissue of the fish that were comparable to the fish in the river, indicating their results are probably biologically relevant. They found that the fish exposed to the drug exhibited increased activity, reduced sociality, and higher feeding rate relative to control fish.

Although they scuffed their experiment a little with their choice of concentrations, they did do something that few other ecotoxicology studies do. They looked at behavioural traits that are important for the survival of fish in the wild. Too slowly are excotoxicologists moving away from testing the lethal effects of pollutants, often requiring doses that never occur in the wild. Hopefully, the publication of the Brodin et al. paper in the prestigious journal Science will encourage more researchers to examine the effects of pollutants at the levels which they typically occur and on a greater range biologically interesting traits.

References:

Kidd, K., Blanchfield, P., Mills, K., Palace, V., Evans, R., Lazorchak, J., & Flick, R. (2007). Collapse of a fish population after exposure to a synthetic estrogen Proceedings of the National Academy of Sciences, 104 (21), 8897-8901 DOI: 10.1073/pnas.0609568104  

Kasprzyk-Hordern, B., Dinsdale, R., & Guwy, A. (2009). The removal of pharmaceuticals, personal care products, endocrine disruptors and illicit drugs during wastewater treatment and its impact on the quality of receiving waters Water Research, 43 (2), 363-380 DOI: 10.1016/j.watres.2008.10.047  

Rey, Z., Granek, E., & Buckley, B. (2011). Expression of HSP70 in Mytilus californianus following exposure to caffeine Ecotoxicology, 20 (4), 855-861 DOI: 10.1007/s10646-011-0649-6  

Rodriguez del Rey, Z., Granek, E., & Sylvester, S. (2012). Occurrence and concentration of caffeine in Oregon coastal waters Marine Pollution Bulletin, 64 (7), 1417-1424 DOI: 10.1016/j.marpolbul.2012.04.015  

Brodin, T., Fick, J., Jonsson, M., & Klaminder, J. (2013). Dilute Concentrations of a Psychiatric Drug Alter Behavior of Fish from Natural Populations Science, 339 (6121), 814-815 DOI: 10.1126/science.1226850