Tracking contaminants in Australia’s rivers


We rarely think about what happens to the soap that runs down the drain as we wash our hands. And what about the last bit of that cold coffee that we dump out before washing the cup? It turns out the compounds we wash down the drain without a second thought can end up quite far away, with traces of our everyday lives showing up in rivers and streams.

researcher and equipment next to river

Much research has focused on contaminants in wastewater and effluent at treatment plants. But researchers from Australia and New Zealand wanted to look at the fate of some common compounds in the environment. In a new study published in the September-October issue of Journal of Environmental Quality, they measured the concentrations of 42 different contaminants in rivers throughout Australia. Contaminants included industrial compounds, pesticides, pharmaceuticals, and personal care products. While high levels of contaminants were rare, some compounds were widespread and found in unexpected areas.

When contaminants are found in river water, blame can easily fall on wastewater effluents as the source of those compounds. However, the compounds could be coming from other sources, such as industrial discharges, stormwater runoff, and agricultural activity.

“If the compound is present in water due to leaking septic tanks or urban stormwater runoff, a potentially costly upgrade of wastewater treatment plants would not reduce its occurrence,” explains Frederic Leusch, one of the authors of the study and a senior lecturer at Griffith University. “Understanding the sources of different trace organic contaminants in the environment is important to decide on the right course of action.”

To find those sources, Leusch and his co-authors sampled water from 73 river sites across Australia. They chose sites that reflected a variety of land uses and different areas around the country. “We selected sites to evenly represent five main types of activities: agricultural areas, zones of industrial activity, urban residential areas, sites close to wastewater discharges, and reference sites which we called undeveloped,” says Leusch.

aerial view of winding river

The scientists sampled the various locations over one year and analyzed the samples for contaminants. They found two compounds in over half of the samples – salicylic acid and caffeine. Salicylic acid, found in 82% of samples, is metabolite of aspirin. It is also a plant hormone found in several species including willows, which are commonly found near Australian streams. Caffeine was found in 65% of the samples. Because caffeine is metabolized by people and excreted as a different compound, finding it in so many samples points to a more direct source. Leusch suggests that it could be traced to people pouring unfinished coffee pots down the drain or hikers doing the same into small rivers and streams.

In addition to finding the most common compounds, the researchers wanted to know if any of the compounds were at concentrations high enough to cause health concerns.  To determine this, the researchers calculated a hazard quotient. The quotient is the highest concentration of each compound they found divided by a concentration which is known to be safe. A hazard quotient above one meant that the compound was present at least once at a concentration that could be of concern.

Neither salicylic acid nor caffeine had hazard quotients near one, so they do not pose a significant threat to the environment. Only three compounds had hazard quotients above one – simazine, an herbicide; carbamazepine, a drug used to treat epilepsy; and sulfamethoxazole, an antibiotic. While all of these compounds need further attention, Leusch notes that the antibiotic is of specific concern. Not only is it an environmental risk, but it could also lead to instances of antibacterial resistance.

The researchers were also interested in how various land uses would affect which contaminants they found. While a few compounds were found more often in some areas than others, Leusch and his co-authors were surprised that there were not clearer links between land use and contaminants.

researcher on bank of river

“For example,” explains Leusch, “we expected pesticides to be more common in agricultural areas, but they were present in most areas. Or pharmaceuticals and personal care products to be more common in areas that receive wastewater. But we found them frequently at pretty much every type of site we looked at – including our undeveloped site.”

There are likely two reasons for the lack of clear links between land use and contaminants. First, it was difficult for researchers to distinctly categorize sites. Most sites received input from several sources, such as agriculture and industry. Also, many chemicals are used in more than one category of site. Pesticides, for instance, are used in agriculture but also by the public in their gardens.

A better understanding of the sources of these compounds found at multiple sites is the focus of future research for Leusch and his colleagues. As scientists work to pinpoint sources, Leusch suggests consumers think about the products they’re using. For example, disposing of pharmaceuticals properly and avoiding products with unnecessary antimicrobials could help reduce contamination.

“While our results do not particularly raise any major red flags,” he says, “I think the consensus is that there are a few compounds out there that really don’t need to be there.”



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