Much has been made recently of the impact of sewage overflows into freshwater environments; it’s a hazard to human health and the environment that is rightly of great concern. However, the risk is that in focusing on this threat to waterways, we fail to address wider problems that bypass wastewater treatment altogether.
Freshwaters support among the greatest concentrations of biodiversity of all the ecosystems on the planet. They are also some of the most endangered, losing biodiversity faster than any other ecosystem.
Only 14 per cent of English rivers have good ecological status and not one is free from chemical contamination. Plastic pollution, untreated sewage, agricultural waste, excessive abstraction and climate change are well-documented threats, evidenced in the loss of freshwater life.
To add to these hazards, in the last decade virtually every river across the globe has been found to contain some mix of common drugs such as ibuprofen, paracetamol and diclofenac.
These medicines have only recently started to be considered in water-quality testing and their effects in the environment are poorly documented. Sources include residues from medicines that pass, unused, through our bodies, or excess medicines that have been disposed of incorrectly, flushed or washed into the sewerage system, to eventually end up in our rivers.
A recently published global study measured concentrations of pharmaceuticals at more than 1,000 sites along 258 rivers and in 104 countries, covering all continents. Only two study sites were unpolluted from pharmaceutical compounds.
The study highlights the direct impact this pollution has on the environment, but also a global threat from this pharmaceutical pollution to human health.
More than 4,100 invertebrate species spend at least part of their lifecycle in freshwater in the UK. They deserve more of our attention. They include well-known freshwater invertebrates such as dragonflies, mayflies, pond skaters and water beetles.
These species play a vital role in maintaining clean water, recycling organic matter and providing a food source for fish, birds, and mammals. The presence of aquatic insects is the standard indicator of the health of freshwaters.
Maintaining invertebrate populations is essential. Although they play a fundamental role in ecosystems, they are also affected by changes in their environment. Current rates of decline could see 41 per cent of the world’s invertebrate species becoming extinct over the next few decades.
Aquatic species are faring worst, at 33 per cent threatened compared to 28 per cent of terrestrial species. In the UK a long-term study of rivers in Wales found freshwater invertebrates becoming extinct twice as fast as species in any other ecosystem.
Threats to aquatic invertebrates include pollution, invasive non-native species, climate change, habitat loss and water extraction. Pollution sources include domestic and industrial sewage effluents and run-off from agriculture and urban areas. And pesticides pose a particular risk to freshwater ecosystems.
Introducing invasive non-native species to new ecosystems has also reduced species richness and abundance; mayflies, caddisflies, freshwater shrimps and other crustaceans are particularly vulnerable. And climate change is changing water temperatures and flow, two things that species including mayflies, caddisflies, and stoneflies need to be finely balanced.
Buglife’s latest research investigates the presence and impact of human pharmaceuticals on freshwater invertebrates. It considers the steps we can take to reduce their effect on the environment.
Medicines are essential to the health of humans and domesticated animals. They help us to survive infection, reduce pain and eradicate disease. However, some of these medicines can be harmful to the environment.
Diclofenac, a pain killer and anti-inflammatory, is perhaps the best-known environmentally harmful medicine; its effects are dramatic and obvious.
Diclofenac led vulture populations in Asia to become extinct and is threatening recovering European vulture populations. Diclofenac is used to treat livestock but is highly toxic to vultures, who consume it when they feed on carcases of treated livestock.
In freshwater invertebrates, effects tend to be more subtle. Changes in development, reproduction and behaviour are the most common. Although they are not always lethal, these changes can lead to shifts in evolution and populations structure in ways that damage the species.
One of the main sources of these medicines is wastewater treatment works (WWTWs), few of which process medicines efficiently. By examining data from the most recent chemical-investigation programme (CIP2), Buglife found WWTWs are responsible for increased concentrations of certain medicines in downstream surface waters.
Buglife also found that several medicines regularly occur at concentrations greater than current predicted no-effect concentrations (PNECs), both upstream and downstream of WWTWs.
In the case of several drugs that the report looked at, there is evidence that invertebrates are affected at concentrations below PNEC limits, including the drugs carbamazepine, propranolol, ibuprofen, venlafaxine and fluoxetine.
Depending on the chemical detected, the effects include stress responses, increases or decreases in invertebrate reproduction, changes in behaviour that could lead to greater predation and damage to living cells.
But scientists have also found that when medicines break down in the environment, they can produce chemicals that are many times more harmful than the original chemical alone. Diclofenac becomes six times more toxic to algae, an important source of food for grazing invertebrates such as snails, mayfly and caddisfly larvae.
When naproxen – another anti-inflammatory drug – breaks down, it prevents the reproduction of small crustaceans and algae at concentrations four to 16 times lower than those of the original chemical.
Our review of current literature and analysis of the second phase of CIP2 data suggests that the main chemicals of concern to invertebrates are:
This non-steroidal, anti-inflammatory medication is pervasive, found in all surface waters exceeding safe limits and recorded to occur at concentrations that impact invertebrates
This anti-epileptic medication appears to affect invertebrates at levels in the environment
below the current safety standards
This anti-depressant medication occurs in the environment at concentrations observed to alter invertebrate behaviour and reproduction. It is also known to bioaccumulate
This anti-depressant medication is not included in CIP2 sampling but causes stress responses in the freshwater snail, Leptoxis carinata, at concentrations well below the safety standard
This non-steroidal anti-inflammatory medication is poorly eliminated through WWTWs and commonly occurs in surface waters above safe limits. It is known to bioaccumulate in invertebrates and can impact some avian species.
Pets and pesticides
Pharmaceuticals are just the latest on a long list of chemicals found to impact invertebrates in our waterways. In 2020 researchers at the University of Sussex found widespread contamination of English rivers from two neurotoxic pesticides that commonly used in veterinary flea products.
Fipronil and the neonicotinoid imidacloprid are highly toxic to all insects and other aquatic invertebrates. These chemicals are banned for agricultural use, due to their adverse environmental effects, but there is minimal environmental risk assessment for using them to treat domestic cats and dogs.
This reflects the assumption that there will be fewer environmental impacts as these spot treatments contain only a small amount of product. But data gathered by the Environment Agency in English waterways between 2016-2018 found fipronil in 98 per cent of freshwater samples and imidacloprid in 66 per cent.
As with human medicines, WWTWs are an important route to waterways. These chemicals end up in our sewers when we bathe pets treated with spot-on fipronil flea products and when we wash our hands, pet bedding and other surfaces with which treated pets have had contact.
Other pathways to contaminating our waterways include treated pets swimming in waterbodies and rainfall wash-off. The strong correlation between fipronil and imidacloprid levels across the river sites tested indicates a common source.
Even minor traces of pesticides can impact non-target species and habitats such as freshwaters. Neonicotinoids are known to wash off seeds and are taken up by wildflowers, where they poison bees and other pollinators, and travel through the soil polluting rivers and harming mayflies and other aquatic invertebrates.
In 2016, the River Waveney was acutely and chronically polluted with neonicotinoid insecticides. The most likely source was run-off from sugar beet fields in the catchment.
We need urgent action to evaluate the long-term effects of medicines and other chemicals in the environment. The biggest concern with pharmaceuticals is how long they have gone unchecked; we simply do not know how much damage they are causing.
Experiments carried out at concentrations found in the environment are rare. However, research has found that with some drugs, the adverse effects increase with time, so that small amounts can cause the same effects over a long period.
Other drugs, including the antibiotic azithromycin, have not been assessed at all – we simply do not know what effects they have on invertebrates and the wider environment.
Medical drugs are monitored, but have little to no enforced environmental regulation. We need to improve evaluation of the environmental risks that medicines pose, including retrospective risk assessments for existing drugs.
We also need to conduct environmental assessments of breakdown products and of the effects of mixing chemicals as these are often far greater than the impacts of individual substances.
As wastewater treatment plants are both the source and easiest point from which to manage pollution, we must improve processes to stop chemical pollutants entering the environment in the first place.
We also need closer scrutiny of other sources of contamination – septic tanks, sewer overflows, river and pond sediments, biosolids, landfill run-off and agricultural run-off.
We need to prevent pollutants entering the environment and, where possible, reduce the number of medical drugs that enter our waterways before treatment.
One solution is better education about how to use and dispose of medical drugs. Another is to improve regulation to tackle sources that generate the worst impacts.
And perhaps this research highlights other, nature-based opportunities. We have a growing body of scientific evidence to show that medicine isn’t always the best answer. Drug-free approaches such as blue-green social prescribing – spending more time in nature to protect our health – could perhaps also help us to protect our environment.
Download the Pharmaceuticals in Freshwater report and find out about Buglife’s work at www.buglife.org.uk. David Smith is social change and advocacy officer at Buglife – the invertebrate-conservation trust
This story was first published in The Environment magazine in May 2022
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