• Aucun résultat trouvé

SOURCES AND PATHWAYS OF PHARMACEUTICALS INTO THE ENVIRONMENT

Dans le document The DART-Europe E-theses Portal (Page 36-40)

CHAPTER 2: PHARMACEUTICALS IN THE WATER CYCLE

2.2 SOURCES AND PATHWAYS OF PHARMACEUTICALS INTO THE ENVIRONMENT

The sources and pathways of pharmaceuticals into the environment have been identified for quite some time.

Indeed, they are explored in most of the reference cited in the previous section. The issue has been summarized by some publications (Heberer, 2002; Ritter et al., 2002; Santos et al., 2010; Qian et al., 2015) which proposed very similar diagrams with some variations.

A short summary of those articles and a new diagram that represent the dispersion of pharmaceuticals into the environment is proposed (figure 1).

Figure 1: Dispersion of pharmaceuticals in the environment: sources and pathways. Black arrows represent the main pathways. Grey arrows represent secondary pathways. Pathways on which pharmaceuticals are removed (i.e. incinerators) are not represented.

Whether they are for human or veterinary purposes, pharmaceuticals products are manufactured in specialized factories. It has been reported that pharmaceuticals molecules can be found in the effluents of these factories.

Sometimes, the effluents are directly discharged into surface water or they can be redirected to WWTPs.

Veterinary products are used almost completely for livestock (farming and aquaculture). They are used for diseases treatment and prevention and in some countries for growth. A small proportion of veterinary products are used for pet animals that can excrete pharmaceuticals almost everywhere (ground, surface water or sewer via drained surfaces). Animals metabolize pharmaceuticals and eventually excrete a certain fraction of the molecule unchanged via urine and faeces. The fate of urine and faeces differs depending on the type of animal.

They can be discharged into surface water (open-sea aquaculture, run-off from farms or land application), infiltrated in the ground and eventually groundwater (farms) or sometimes drained and directed to a WWTP.

Products for human uses are distributed via domestic circuits (pharmacies) or healthcare facilities (all types of hospital, nursing home…). The importance of hospitals, as places of high pharmaceuticals consumption, has been studied intensively. Most of the time, hospital wastewater is more concentrated in pharmaceuticals than domestic ones, but their loads are much lower. This is, however, not true for large hospitals connected to small WWTPs, and for pharmaceuticals that are preferably or exclusively consumed in hospitals. Consumed pharmaceuticals are metabolized by humans and a certain fraction is excreted as unchanged molecules. Then, it is either discharged to a sewer system or a septic tank. Pharmaceuticals eventually leaks from septic tanks to the ground and groundwater. Sewers transport pharmaceuticals to a WWTP. However, pharmaceuticals can reach surface water, the ground and ground water if the sewer system has leaks or in case of overflows (storm, dysfunctional pumping stations…). Unused pharmaceuticals are either discharged to sinks and endure the same fate as metabolized pharmaceuticals, collected with garbage and put in landfill or eliminated in incinerators, or collected via special programs for unused pharmaceuticals and eliminated. Unused pharmaceuticals stored in landfills can eventually leach to the ground and groundwater.

At the WWTP, the collected pharmaceuticals are unequally transformed. Traditional WWTPs were not design to remove such molecules, thus their efficiency towards pharmaceuticals is very variable. A fraction of them are discharged with WWTPs effluents into surface water. Another fraction is concentrated in sludge and can be either incinerated or used in agriculture. From there it either reaches the ground and infiltrates to groundwater or reaches surface waters via run-off.

In the environment, pharmaceuticals can pass from surface water to groundwater (infiltration or managed aquifer recharge) and the other way around (exfiltration).

Lastly, via drinking water treatment plants, pharmaceuticals could be redirected everywhere. Also, products from livestock and agriculture could be contaminated by pharmaceuticals and reach humans.

In every step, pharmaceuticals are susceptible to be transformed (sorption to solids and biofilms, degradation by solar exposition, absorption by wildlife or plants…). Such transformations are seldom studied, especially concerning in-sewer processes.

This cycle strongly depends on each country context. Pharmaceuticals consumption differs, as does sewage management. However, in western countries, the main source of pharmaceuticals is considered to be human consumption, excretion to sewers and discharge to surface water after treatment at the WWTPs. Discharge into surface water and infiltration to groundwater of veterinary products is considered another non negligible source. Still, each pathway can have a significant impact on certain locations.

2.3 RISK OF PHARMACEUTICALS CONTAMINATION Pharmaceuticals effects on living organisms are:

Acute or chronic: if an organism reacts when exposed one time to a specific concentration of a pharmaceutical, the effect is acute. However, if the organism only reacts when exposed for a prolonged time or repetitively, the effect is chronic.

Deterministic or stochastic (Ritter et al., 2002): “effect for which the severity of the damage caused is proportional to the dose and for which a threshold dose exists below which they do not occur are called deterministic effects. […], effects for which the probability of occurrence, rather than severity, is proportional to the dose are referred to as stochastic effects.”

These distinctions make the determination of the risk of pharmaceuticals very difficult. Lethal effects are not the only effects that are targeted, sub-lethal effects (malformations, immobilizations, changes in behavior) are also critical to understand the hazard of pharmaceuticals.

Effects of pharmaceuticals on humans are observed… In fact, that is what they were designed for. But, it’s happening at relatively high doses, most of the time at a few hundred mg. In comparison such doses represent a large volume of wastewater since their pharmaceuticals concentrations are never greater than a few hundred µg/L, and an even larger volume of environmental or drinking water. However, chronic exposure to low concentrations of many pharmaceuticals could be harmful, even if it has not been observed yet and in addition with all other pollutants present in the water. Increases of antibiotic-resistant micro-organism populations, hormonal perturbations, cancers frequencies or frequencies of allergies are possible (Kümmerer, 2016).

Concerning wild life, the situation is a bit different. Populations of vultures in south Asia have declined after ingestion of Diclofenac (Green et al., 2004; Oaks et al., 2004; Shultz et al., 2004). Population of fish feminized in Lake Ontario (Canada) after exposition to synthetic estrogen (Kidd et al., 2007). Fish changed behavior (much more aggressive) after exposition to Oxazepam in Sweden (Brodin et al., 2013).

Apart from those spectacular examples, the challenges of pharmaceuticals risk studies are still important.

Studies on chronic effects are scarce (Santos et al., 2010). Normalizing the uses and interpretations of eco- toxicological tests focusing on sub-lethal effects has to be done, especially for studying “cocktails” of pharmaceuticals (Vasquez et al., 2014) and/or with other pollutants.

Dans le document The DART-Europe E-theses Portal (Page 36-40)