Determination of microplastic polyethylene (PE) and polypropylene (PP) in environmental samples using thermal analysis (TGA-DSC)

Microplastics are increasingly detected in the environment and the consequences on water resources and ecosystems are not clear to date. The present study provides a cost-effective and straightforward method to determine the mass concentrations of polymer types using thermal analysis. Characteristic endothermic phase transition temperatures were determined for seven plastic polymer types using TGA-DSC. Based on that, extracts from wastewater samples were analyzed. Results showed that among the studied polymers, only PE and PP could be clearly identified, while the phase transition signals of the other polymers largely overlap each other. Subsequently, calibration curves were run for PE and PP for qualitative measurements. 240 and 1540mg/m3 of solid material (12µm to 1mm) was extracted from two wastewater effluent samples of a municipal WWTP of which 34% (81mg/m3) and 17% (257mg/m3) could be assigned to PE, while PP was not detected in any of the samples. The presented application of TGA-DSC provides a complementary or alternative method to FT-IR analyses for the determination of PE and PP in environmental samples

Antibacterial Activity of Sulfamethoxazole Transformation Products (TPs): General Relevance for Sulfonamide TPs Modified at the <i>para</i> Position

Sulfonamide antibiotics undergo transformation in the aquatic environment through biodegradation, photolysis, or hydrolysis. In this study, the residual antibacterial activity of 11 transformation products (TPs) of sulfamethoxazole (SMX) was investigated with regard to their <i>in vitro</i> growth and luminescence inhibition on Vibrio fischeri (30 min and 24 h exposure). Two transformation products, 4-hydroxy-SMX and <i>N</i>⁴-hydroxy-acetyl-SMX, were synthesized in-house and confirmed by nuclear magnetic resonance and high-resolution mass spectrometry. Results of individual compound experiments showed that TPs modified at the <i>para</i> amino group still exhibit clear antibacterial effects, whereas TPs resulting from breakdown of the SMX structure lost this mechanism of action. 4-NO₂- and 4-OH-SMX were found to inhibit growth to a clearly greater extent than the parent compound, SMX. In contrast, the <i>N</i>⁴-acetyl- and <i>N</i>⁴-hydroxy-acetyl-derivatives retain less than 10 and 5% of the effect of SMX on growth and luminescence inhibition, respectively. The effect of a mixture of <i>para</i>-modified TPs was observed to be additive. Considering the homologous series of sulfa drugs widely prescribed and their common mechanism of action, the potential environmental impact must consider the total amount of sulfonamide antibiotics and their derivative TPs, which might end up in a water body. Extrapolating the results obtained here for the <i>para </i>TPs of SMX to other sulfa drugs and determining the persistence and occurrence of these compounds in the aquatic environment is required for improved risk assessment