A critical assessment of the photodegradation of pharmaceuticals in aquatic environments: defining our current understanding and identifying knowledge gaps

Abstract

This work presents a critical assessment of the state and quality of knowledge around the aquatic photochemistry of human- and veterinary-use pharmaceuticals from laboratory experiments and field observations. A standardized scoring rubric was used to assess relevant studies within four categories: experimental design, laboratory-based direct and indirect photolysis, and field/solar photolysis. Specific metrics for each category are defined to evaluate various aspects of experimental design (e.g., higher scores are given for more appropriate characterization of light source wavelength distribution). This weight of evidence-style approach allowed for identification of knowledge strengths and gaps covering three areas: first, the general extent of photochemical data for specific pharmaceuticals and classes; second, the overall quality of existing data (i.e., strong versus weak); and finally, trends in the photochemistry research around these specific compounds, e.g. the observation of specific and consistent oversights in experimental design. In general, those drugs that were most studied also had relatively good quality data. The four pharmaceuticals studied experimentally at least ten times in the literature had average total scores (lab and field combined) of ≥29, considered decent quality; carbamazepine (13 studies; average score of 31), diclofenac (12 studies; average score of 31), sulfamethoxazole (11 studies; average score of 34), and propranolol (11 studies; average score of 29). Major oversights and errors in data reporting and/or experimental design included: lack of measurement and reporting of incident light source intensity, lack of appropriate controls, use of organic co-solvents in irradiation solutions, and failure to consider solution pH. Consequently, a number of these experimental parameters were likely a cause of inconsistent measurements of direct photolysis rate constants and quantum yields, two photochemical properties that were highly variable in the literature. Overall, the assessment rubric provides an objective and scientifically-defensible set of metrics for assessing the quality of a study. A major recommendation is the development of a method guideline, based on this rubric, for conducting and reporting on photochemical studies that would produce consistent and reliable data for quantitative comparison across studies. Furthermore, an emphasis should be placed on conducting more dual-fate studies involving controlled photolysis experiments in natural sunlight, and whole system fate studies in either natural or artificial systems. This would provide accurate data describing the actual contribution of photolysis to the overall fate of pharmaceuticals in the environment.

Removal of pharmaceuticals and personal care products from wastewater using algae-based technologies: a review

“…Free radicals are generated with the presence of photosensitizer such as chromophoric dissolved organic matters (CDOMs), NO 3 -, carbonate, and certain metal ions (Boreen et al 2003). Indirect photolysis are generally more important for the overall fate of PPCPs in natural waters and wastewater due to the ubiquitous presence of photosensitizers, especially for those without significant absorption of light above 290 nm (Challis et al 2014). Rate of sunlight induced photodegradation can be related to the latitude and varies seasonally due to angle and duration of the solar irradiance, and more rapid photodegradation can be expected during summer time in low latitude area (Andreozzi et al 2003).…”

“…In direct photolysis, target compound is broken down by absorbing incident light directly. PPCPs with aromatic rings, conjugated p systems, heteroatoms, and other functional groups can be prone to direct photolysis due to a strong absorption of irradiation within the UV range of the sunlight (Challis et al 2014). However, indirect photolysis occurs with the generation of free radicals such as hydroxyl radicals (OHÁ), peroxyl radicals (ROOÁ), and singlet oxygen ( 1 O 2 ) produced during sunlight illumination.…”

Medicines, shaken and stirred: a critical review on the ecotoxicology of pharmaceutical mixtures

“…[9]), and most pharmaceuticals will either be transformed by physical and chemical processes and/or are biotransformed to a broad mélange of chemicals with often unknown ecotoxicological properties (see reviews, e.g. in [10][11][12]). All these factors add additional layers of chemical complexity, which in total poses a formidable challenge for the hazard and risk assessment of pharmaceuticals for environmental organisms, usually exposed over their whole life cycle (see also [13,14]).…”

Investigating the Influence of Some Environmental Factors on the Stability of Paracetamol, Naproxen, and Diclofenac in Simulated Natural Conditions

“…In surface waters, pharmaceuticals undergo sorption and desorption on molecules of organic matter and sediments, transformations by bacteria, and direct or indirect photodegradation in the surface layers [1,12]. Stability of pharmaceuticals in water environments depends on a number of factors, in particular on the intensity of light, but also on the presence of suspended organic matter and the concentration of inorganic ions such as CO 3 2-, HCO -3 , NO 3 -, Fe 2+ , and Fe 3+ [13][14]. The aim of the presented study was to analyze the impact of selected environmental factors (humic acids, NO 3 -and NO 2 -ions, solar light intensity, and ambient pH) on the stability and kinetics of photo-reactions in three compounds belonging to the family of non-steroidal antiinflammatory drugs (NSAID): paracetamol, naproxen, and diclofenac (Fig.…”