Pharmaceuticals Quietly Enter Aquatic Ecosystems

Pharmaceuticals and personal care products have been widely detected in surface waters and in fish tissues. A major source of these contaminants is the effluent discharged from urban wastewater treatment plants. Although laboratory experiments have previously examined the toxicity of pharmaceutical pollution in aquatic environments, most of those studies relied on artificially contaminating aquaria to observe fish responses. In contrast, far fewer investigations have examined how these substances accumulate within organisms under real environmental conditions. To address this gap, researchers sampled seven creeks and rivers in the state of Victoria, Australia. By analyzing pharmaceutical concentrations in both water and fish tissues, the study sought to determine the extent of environmental exposure and the potential for biological accumulation.

Pathways of Pharmaceutical Contamination in Water（圖片來源：Papaioannou C et al，採用 CC BY 4.0 授權）

Sampling results showed that twelve pharmaceuticals were detected in environmental waters. These compounds included antidepressants, antihypertensive drugs, analgesics, and caffeine. Among them, the antidepressant venlafaxine was present at the highest concentration, reaching 0.97 µg/L in surface water. In samples collected directly from wastewater treatment plant effluent, venlafaxine concentrations were even higher, reaching 1.4 µg/L. Pharmaceutical concentrations also displayed a spatial gradient: the highest values occurred at contamination hotspots near discharge points, followed by downstream sites, while upstream sites generally had the lowest concentrations.

Fish analysis included 131 individuals representing five medium- to large-sized species: Anguilla australis, Perca fluviatilis, Gadopsis marmoratus, Cyprinus carpio, and Tinca tinca. Pharmaceutical residues were detected in 27% of the sampled fish. The highest recorded concentration of venlafaxine reached 150 µg/kg in the muscle tissue of Perca fluviatilis. Another antidepressant, sertraline, was detected in Anguilla australis at concentrations up to 100 µg/kg. Additional compounds identified in fish tissues included carbamazepine (an antiepileptic drug) with concentrations up to 39 µg/kg, triclosan (a preservative) up to 40 µg/kg, and caffeine up to 82 µg/kg.

By comparing drug concentrations in water and fish tissues, researchers calculated bioaccumulation factors for different species and compounds. These calculations revealed substantial variation among species. In Anguilla australis, the bioaccumulation factor for sertraline reached as high as 3,333 L/kg, indicating strong accumulation capacity. In Perca fluviatilis, venlafaxine bioaccumulation ranged between 104 and 341 L/kg, while carbamazepine reached up to 520 L/kg. Although Cyprinus carpio and Gadopsis marmoratus showed relatively lower detection levels overall, their bioaccumulation factors for caffeine were still notable, in some cases exceeding 8000 L/kg.

The study also conducted two types of risk assessment: one focusing on potential human health risks and another evaluating ecological risks to aquatic environments. For human health assessment, two consumption scenarios were considered: adults consuming either one or twelve servings of fish per month. Researchers compared the estimated intake of pharmaceuticals from fish consumption with the minimum therapeutic dose used in medical treatment, expressed as the margin of exposure (MOE). The results indicated that all detected pharmaceutical exposures were far below clinically relevant doses. Even under the high-consumption scenario, the intake of venlafaxine and sertraline remained more than 8000 times lower than their therapeutic doses, suggesting extremely low risk to human health.

The ecological risk assessment produced a more concerning picture. Certain pharmaceuticals were found at levels capable of posing risks to aquatic organisms. Carbamazepine concentrations in particular reached levels considered potentially harmful to fish and other aquatic life. Other compounds, including trimethoprim (an antibiotic), propranolol (an antihypertensive drug), sertraline, and venlafaxine, were classified as having moderate ecological risk potential. These findings highlight an important distinction: substances that appear safe for human consumption may still exert meaningful ecological impacts.

Indeed, previous studies have shown that pharmaceuticals such as venlafaxine, sertraline, and carbamazepine can influence fish embryo development, neural signaling pathways, and social behavior. Although such effects may not cause immediate mortality, subtle behavioral changes can have long-term ecological consequences. Fish exposed to these compounds may show reduced responses to predators, making them easier targets. Social behaviors may become abnormal, leading to isolation from groups or increased aggression. Feeding behavior may also change, resulting in uncontrolled feeding or ingestion of inappropriate materials. Reproductive behavior can be disrupted as well, with fish failing to build nests, protect eggs, or display normal courtship behaviors.

Most pharmaceuticals are organic molecules and can eventually degrade in natural environments. However, when the rate of contamination exceeds the rate of degradation, these compounds can accumulate within aquatic organisms. Such accumulation raises the possibility of transfer through food webs, potentially affecting waterbirds or mammals that consume contaminated fish. What appears to be trace-level pollution in the environment may therefore carry substantial ecological significance, particularly when long-term accumulation and mixture effects are taken into account.

Author: Shui-Ye You

Reference:

Saaristo M et al. (2024). Pharmaceuticals in biota: The impact of wastewater treatment plant effluents on fish in Australia. Environmental Pollution.