High concentrations of the anti-inflammatory drug diclofenac have been detected in the marine environment around False Bay, Cape Town.
According to a first-of-its-kind study, at one sampled site, diclofenac and phenytoin were found in the highest concentrations in an edible seaweed species called sea lettuce. The researchers found that diclofenac, which is sold under the brand name Voltaren, was the most dominant compound detected in seawater, sediment, marine invertebrates (starfish, limpets, mussels, sea urchins and sea snails) and seaweed samples at eight sampled sites around the semi-enclosed bay.
“With these high levels in seaweed, the health impact of using contaminated seaweeds for food and medicinal purposes should be considered. The risks associated with exposure to these compounds, among others, include increased cancer risk, decreased fertility, and effects on the immune system,” the study says.
Professor Leslie Petrik, the group leader of environmental and nano sciences at the University of the Western Cape’s chemistry department, and researcher Cecilia Ojemaye tested levels of pharmaceuticals and personal care products in the near-shore environment of False Bay.
“If you’re harvesting mussels off the rocks at Muizenberg, Hout Bay and Camps Bay, you will certainly get these toxins in [them]. And there are quite a few people who also harvest seaweed,” said Petrik.
Diclofenac was found in higher concentrations than the other persistent chemical compounds, which included sulfamethoxazole (an oral antibiotic), carbamazepine (used to treat epilepsy) and acetaminophen (a pain reliever), as well as being present in almost all the sites where samples were taken.
This didn’t come as a surprise, “considering the high prescription of diclofenac as an anti-inflammatory drug around this region”, coupled with the fact that it is one of the over‐the‐counter medications available as tablets or ointments to treat inflammation and pain.
As a result, the scientists say, public consumption is not regulated by the government or the medical profession.
The researchers describe how the accumulation of pharmaceuticals and personal care products in the different species of organisms reflects the increasing anthropogenic (human-caused) pressure taking place at sampling sites along False Bay, because of population growth and residents’ lifestyle, as well as poorly treated sewage effluent discharge from several associated wastewater treatment plants.
Acetaminophen (used to treat mild to moderate pain) was also observed to be dominant in seawater, sediment and the marine plant and animal life samples. This may be because of the availability of these compounds as non-prescription drugs that can be obtained freely from most pharmaceutical retail outlets, their overuse by consumers and their incomplete metabolism in the body after consumption.
The authors say their results underline the “ubiquitous presence” of diverse selected persistent contaminants from various sources in False Bay.
“The high detection frequency of compounds demonstrates the widespread and direct impact of poorly treated wastewater on the marine environment of False Bay and clearly highlights the significance of non-riverine inputs of sewage into coastal environments,” the study found.
“The trouble is that we are finding unmetabolised pharmaceuticals,” Petrik told the Mail & Guardian. “That basically means those pharmaceuticals are coming in from humans and are being excreted in the waste and the sewage plants are not taking those pharmaceuticals out sufficiently. The amount of unmetabolised medication we’re finding in the marine environment is really very worrying.
“Diclofenac is one of the compounds that is definitely not being removed by the wastewater treatment plants and we’re finding very high levels of diclofenac in the marine water,” she said.
“We know the pharmaceuticals are in the wastewater treatment plants, because we have tested the plants for those same compounds. The usage of those pharmaceuticals is well documented; it is also documented that they are found in the sewage influent and effluent. There can be no doubt these chemicals are coming from the wastewater treatment plants, because nobody discards pharmaceuticals in a stormwater drain.”
The researchers describe how chemicals of emerging concern, such as
pharmaceuticals and personal care products in different water bodies have been a major global issue for years, because of their daily use by millions of people.
Most of these compounds have become continuously present in the ecosystem.
Residues in the environment may pose greater risks to wildlife and ecological health compared to human health.
Although they are usually found at low environmental concentrations, many are of toxicological concern, particularly because of the combined effects of multiple contaminants “hence the potential environmental risk caused by these compounds should not be underestimated,” according to the paper.
“These persistent chemical compounds are called forever chemicals, because they don’t degrade,” says Petrik.
“They are like plastics — they last for a very long time. But unlike plastics one can’t see them.”
According to the paper, in False Bay, marine invertebrates are exposed to pollution from seawater and sediment, accounting for higher concentrations of contaminants, because these compounds are continuously discharged, making them persistent in the marine environment.
Across all the sampling sites, marine organisms were found to bioaccumulate pharmaceuticals. “This indicates that pharmaceutical usage by humans and their consequent presence in sewage effluents impacts on the oceanic environment,” the study found.
The presence of antibiotics such as sulfamethoxazole, found in all plant and animal life at the studied sites, can disrupt a number of vital ecological processes in the marine environment as they become toxic to aquatic organisms in False Bay.
Their presence may promote microbial resistance to this antibiotic. Sulfamethoxazole has been reported to enter the marine ecosystem from incomplete biodegraded sewage waste from wastewater treatment plants, as well as from indiscriminate human use.
Petrik says the effect on marine organisms is completely unknown. “The way one determines toxicity is very much geared towards determining toxic levels in humans. Nobody has done careful studies on these organisms,” she said.
The authors say strict measures are required to limit the discharge of sewage effluents containing these contaminants into the marine environment.
“Furthermore, residents of coastal cities need to be sensitised to the need to continuously protect the marine environment from these chemicals by way of modification and changes to their lifestyles to avert the continuous pollution of the marine environment.”