Population growth, increasing affluence, and greater access to medicines have led to an increase in active pharmaceutical ingredients (APIs) entering sewerage networks. In areas with high wastewater reuse, residual quantities of APIs may enter soils via irrigation with treated, partially treated, or untreated wastewater and sludge. Wastewater used for irrigation is currently not included in chemical environmental risk assessments and requires further consideration in areas with high water reuse. This study critically assesses the contemporary understanding of the occurrence and fate of APIs in soils of low and lower-middle income countries (LLMIC) in order to contribute to the development of risk assessments for APIs in LLMIC. The physico-chemical properties of APIs and soils vary greatly globally, impacting on API fate, bioaccumulation and toxicity. The impact of pH, clay and organic matter on the fate of organic ionisable compounds is discussed in detail. This study highlights the occurrence and the partitioning and degradation coefficients for APIs in soil:porewater systems, API usage data in LLMICS and removal rates (where used) within sewage treatment plants as key areas where data are required in order to inform robust environmental risk assessment methodologies.
Under many circumstances chemical risk assessments for pharmaceuticals and other substances are required to differentiate between 'loss' of a chemical from the aqueous phase as a result of abiotic (sorption or precipitation reactions) or biotic (biodegradation) processes. To distinguish only abiotic processes, it is necessary to work under sterile conditions. Reported methods include poisoning the soil with sodium azide, irradiation and autoclaving. However, a key aspect of any testing is the representativeness of the matrix and so any sterilisation procedure needs to ensure that the integrity of the sample is maintained, in particular particle size distribution, pH and organic carbon partitioning potential. A number of controlled laboratory experiments were performed on 3 different types of soil. Results indicated that none of the methods successfully sterilised the soils and some physico-chemical changes in soils were identified post-treatment. Autoclaving destroyed the soil structure, therefore potentially affecting its sorption behaviour and sodium azide changed the pH of the loam soil solution by 0.53 pH units. Gamma irradiation exhibited least disruption to the tested soils physico-chemical properties. It was therefore concluded that gamma irradiation was the best available method for sterilising soils in preparation for sorption-desorption experiments; however care needs to be taken with this method to ensure that microbial activity is absent, or quantified if present. The changes to soils after sterilisation varied depending on the individual soil properties, indicating that soils should be studied on a case-by-case basis.
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