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A circular economy Part One: Stormwater

Updated: Apr 6, 2023

Around the world, including in Australia, people and governments are pushing zero waste policies that ensure the maximum amount of material can be recycled and reused and that minimal amounts of materials are disposed of as waste.

Here at Murrang Earth Sciences, we have been working on projects at the interface of waste and chemical contamination. Through this work we’ve noticed that, in some cases, these zero waste policies can create unintended environmental consequences. This is because they fail to account for the environmental risks presented by the chemicals in the products to be reused and recycled. In this series of blogs, I aim to tease out this issue a bit more and highlight the very real hazards presented to both humans and the environment from these chemicals, as well as the regulatory headache the zero waste aim is creating in Australia, where rules prohibiting the use of problem chemicals are not in place. For this blog I am starting with one of the easiest media to study, chemically speaking that is, and one that I think is often overlooked as a source of hazardous chemicals to the environment: that is, water—or, more specifically, stormwater.

A stand-out moment for me at SETAC Australia’s 2021 conference was when Australia’s current Principal Regulator for Industrial Chemicals mentioned research that showed the widely used herbicide and biocide diuron had been found to be a contaminant of urban stormwater in Europe. At the time I was shocked. I had been part of numerous discussions in the past around the better recycling and reuse of water in the Australian landscape in relation to stormwater in particular. Stormwater recycling and reuse options ranged from stormwater detention and retention ponds, to managed aquifer recharge, through to direct discharge into iconic rivers such as the Murray-Darling. None of these conversations considered the potential impact of synthetic pollutants such as diuron on water systems. Once my shock that diuron was being released from cities into aquatic environments in highly regulated European jurisdictions had passed, I realised that surely diuron is not the only synthetic chemical of concern in stormwater; other chemicals must too be discharged into stormwater systems. But what are they and do we need to be concerned?

Shutterstock Photo ID: 412348042. Drainage system in the old franch city

While I have only recently learned of this problem, we’ve known for at least a decade that biocidal chemicals are being leached from building materials by rain and other precipitation. The chemicals are deliberately added to building materials, such as cladding (technically referred to as external thermal insulation composite systems), paint, and renders., For example, the herbicide mecoprop is added to certain bituminous sealing membranes for roofs, while the fungicide carbendazime is added to paint.

Chemicals for which environmental exposure has been causing problems for a while are also found in stormwater, including the organophosphate chemical flame retardants tris(2-butoxyethyl) phosphate (TBEP) and tris(2-chloro-propyl) phosphate (TCPP), which are added to buildings’ insulation materials, particularly when these materials are for industrial or commercial use. In fact, far from being unusual, a large and comprehensive study assessing chemicals of concern in US stormwater found that the concentration of most organic contaminants in stormwater was an order of magnitude higher than the same contaminants in agriculturally impacted streams. These organic contaminants include: chemicals such as the neonicotinoid pesticide imidacloprid, which was detected in both higher concentrations and at a higher frequency than in agricultural run-off; chemicals that seem to be everywhere at the moment, such as the coffee-sourced stimulant caffeine; the insecticide N,N-diethyl-meta-toluamide (DEET); the stimulant nicotine; as well as chemicals that indicate impact from leaking sewage pipes, such as the pharmaceuticals metformin and lidocaine. In fact, the median number of synthetic organic chemicals detected in the stormwater samples collected from around the US in this study was 73, with the median cumulative load of these chemicals being 263 µg/L. And we shouldn’t forget that sometimes it takes just one chemical at sufficient concentrations in stormwater to wipe whole populations of organisms out, with the chemical 6PPD-quinone only recently identified as being acutely toxic to coho salmon populations at concentrations of 0.8 µg/L―a concentration far below that which occurs within both Canadian and US rivers.

The research presented above shows examples of how stormwater can be highly contaminated. In places like Australia, however, a country ravaged by droughts, the imperatives to reuse and recycle stormwater and to discharge stormwater to rivers as environmental flows could not be greater. Unfortunately, this reuse, recycling, and discharge comes with huge environmental hazards that are only poorly mitigated. There are numerous drivers of these hazards, which include:

  • The regulatory systems in developed countries such as Australia that do not sufficiently prevent the use of problematic chemicals such as diuron and imidacloprid or account for the use of these chemicals in environmentally relevant ways.

  • The inadequate risk assessment of many chemicals in decades past that have been grandfathered into use but would now be considered too risky to use.

  • The inadequate testing of chemicals for hazardous properties.

  • The occurrence of chemicals that are now prohibited or for which uses are restricted, but which are found in products and materials that were released prior to restrictions being emplaced, with these products acting as a source of chemicals of concern to the environment.

  • The widespread distribution of sources of chemicals of concern in stormwater (e.g., asphalt, bitumen, tar, tire dust, and building materials) across all urbanised catchments in the world that can act as sources of chemicals of significant concern to aquatic environments.

  • The widespread occurrence of materials that act as sources of contaminants (e.g., roads, down-pipes, and stormwater drains) means that chemical migration from these materials into aquatic ecosystems cannot be practicably mitigated at the source.

  • The lack of acknowledgment that there is a problem prevents remedial action from being undertaken at the receptor (e.g., stormwater retention ponds, and stormwater drains).

  • The inadequate monitoring of aquatic ecosystems for impacts from chemicals in stormwater and the corresponding lack of data on the resulting harm. With the absence of such monitoring data, there’s no impetus for action to mitigate pollution impacts. Scientific methods recently developed are allowing for such impacts to be detected, however, and the types of chemicals being seen in stormwater indicate that impacts will be detected if they are sought.

  • The fact that regulators and society as a whole are overwhelmed by the sheer size of the pollution problem and how to address it.

Despite the information presented above, research addressing chemicals of concern in stormwater is sparse. With the impacts to large animals like coho salmon from 6PPD-quinone and many other aquatic species from many other chemicals, I believe it is highly likely that aquatic species have been lost as a result of urban pollution in Australia. We now have the ability to assess and monitor for such chemicals of concern using metabolomics, non-target analysis, and bioassays, however, and evidence suggests that such assessment is urgently needed as part of the drive to halt extinction. In any case, stormwater is not the only medium that is actively being recovered for reuse in the environment and that has the potential to act as a pathway to pollute vast tracts of land. Food waste is a surprising and under-recognised source of contaminants that I will address in Part Two of this series.


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