Pharmaceuticals in the environment

Routes into the environment

Pharmaceutical residues, be it active pharmaceutical ingredients (APIs) or their metabolites, may enter the environment via different routes:

• Emissions from manufacturing and formulation sites may lead to serious contamination of the surrounding surface waters, especially if no water treatment is in place.

• Normal patient use, via excreta or wash-off. This includes illegal or off-label use.

• Improper disposal of expired or left-over pharmaceuticals.

In countries or regions with sufficient sanitation and waste collection systems, less pharmaceuticals will enter the environment than in countries or regions where this is not the case. Routes into the environment are summarised in this infographic (IMI Premier, 2023).

Normal patient use, metabolism, sewage treatment

After use by the patient, the API may be excreted unchanged in the urine or faeces, or metabolised to new chemical entities, which are subsequently excreted. These metabolites may or may not be pharmacologically active. In regions where sanitation systems are used, APIs and their metabolites enter the sewage system, where they are transported to a sewage treatment plant (STP) or wastewater treatment plant (WWTP). When applying gels or cremes, washing hands after application, showering, or washing of clothes may also lead to substantial emissions directly into water. 

STPs and WWTPs are foremost designed to remove nutrients from wastewater. A part of any pharmaceutical residues is also removed due to degradation or sorption to sewage sludge. However, because STPs are not specifically designed to remove pharmaceuticals, a substantial part of them is not removed, with highly variable removal rates for APIs ranging from 0–100%. Thus, APIs and their metabolites are routinely emitted into aquatic ecosystems. From there, they may adsorb to sediments or leach into groundwater. When (treated) wastewater is used for irrigation, pharmaceutical residues may also end up in soils or crops. 

Part of the removal process in an STP involves sorption to sewage sludge. In some regions, this sludge is spread onto agricultural land as a fertiliser. In this case, soils and crops may also become contaminated with pharmaceuticals.

Some WWTPs are now introducing methods to eliminate APIs and their metabolites. Ozonation is one such treatment (Szabová et al., 2020).

Improper disposal and waste treatment

Expired or leftover pharmaceuticals should be collected and incinerated should there be no other means of reuse. However, collection systems are not always in place and patients do not manage their medicines properly. Improper disposal of expired or leftover pharmaceuticals may then occur via direct flushing of products into the municipal sewage system. 

When expired or leftover pharmaceuticals enter the municipal solid waste management system and this is not incinerated, they will end up in landfills. From there, residues may leach out and contaminate groundwater. Controlled landfill sites should collect leachate, therefore limiting this route to the environment. However, legislation governing this varies country to country and so it remains a concern.