Interaction of sulfathiazole with soils differed by content of organic matter and calcium and its diffusion in real conditions

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Nowadays, the global problem with pharmaceuticals in the environment occurs. Pharmaceuticals are used widely in the world as a treatment in human and veterinary medicine. They are an essential part of the modern world, and their usage increases every year. New and new pharmaceuticals are created and made. But they may have an impact on the environment. Pharmaceuticals are often found in the water and soils in low concentrations (from nanograms to micrograms per liter). Due to overuse, incomplete absorption and metabolism may occur, and an unutilized part of pharmaceuticals is discarded into the environment through urine and feces. Unfortunately, this is not the only way how they can get into the environment. Sometimes they may be unproperly discarded, such as via toilet, drain, or simply thrown into the waste. Many pharmaceuticals, especially antibiotics, are excreted in large quantities as active compounds. There are some of them, especially sulfonamide antibiotics, that aren’t cleared with wastewater treatment and as uncharged forms stay in the water that is often used for watering or fertilizing agricultural soils. After entering the soil, most antibiotics undergo a biological and physicochemical transformation, but they keep their antimicrobial activity and may be potentially toxic to soil bacteria. Not only they can be toxic to bacteria, but they may have an impact on soil enzymes that are essential for the bioavailability of nutrients for plants. If the pharmaceuticals don’t undergo the transformation, they may be adsorbed by soil organic matter and other soil components (for example clay particles). If they are not adsorbed, they are able to diffuse deeper into the soil. For our studies, we used four soils from different parts of the Czech Republic that differed by organic matter or amount of calcium. Two pairs of soils were used, one that differed by the amount of organic matter and calcium, and a pair with different amounts of calcium. Adsorption of pharmaceuticals is dependent on the presence of calcium along with magnesium because they are able to adsorb instead of pharmaceuticals. Therefore, the pharmaceuticals can stay in waters used to treat the soil or in the soil solution. As a model antibiotic, sulfathiazole was used. Sulfathiazole is a sulfonamide antibiotic that it’s no longer used in human medicine but is approved to be used in veterinary medicine. The main problem with this type of antibiotic is, that the majority of sulfonamide antibiotics are able to get through the wastewater treatment in intact condition. Firstly, simple batch sorption/desorption experiments were performed in order to determine sorption characteristics a stability of formed complexes. Following experiments were realized in situ. Plastic tubes were performed to see its behavior in real conditions. These plastic tubes were put into the real soil therefore soil column was isolated from surroundings and covered with filter paper soaked in the drug solution. After different periods, the tubes were taken out of the soil and divided into six layers. These layers were analyzed and the time development of concentration profiles in soil column was obtained. The tap water, distilled water, and MgCl2 were used as leaching agents for drugs. Their concentrations were measured in the leachates. Simultaneously, the soil layers were analyzed in order to determine the content of organic matter. The effective diffusion coefficient including interactions of drugs with soil as well as soil structure were obtained at real circumstances. It is very important to study the behavior of pharmaceuticals in the environment because they release into the soils from more sources (production of pharmaceuticals, wastewater, use of manure for fertilization) and then then they may get into plants and food.

Adsorption, desorption, soil, sulfathiazole, diffusion, organic matter, calcium

ZÁVODSKÁ, P.; SLANINOVÁ, K.; FUČÍK, J.; KLUČÁKOVÁ, M.

7. 8. 2023