Are there pharmaceutical compounds in sediments or in water? Determination of the distribution coefficient of benzodiazepine drugs in aquatic environment

Alprazolam, clonazepam and diazepam are drugs belonging to the benzodiazepine class. These drugs might be important environmental contaminants in aquatic media. A total understanding of behavior and fate of drugs in aquatic environment is not available for these and other drugs. Thus, in this work, a complete optimization of sample treatment and extraction of analytes from sediments and water was described, as well a study of sediment/water distribution comparing it with sample characteristics. Ultrasound for 10 min and 3 steps using 3 mL of extraction solvent were chosen as the stirring form for extraction. A methanol/water (1:1) solution pH 12 was the best extraction solvent. Aiming to eliminate interferences, an addition of 10 μL of NaCl 3.06 mol L−1 was necessary after each step of extraction. Sediment and water samples were characterized, presenting different values on physical-chemical parameters. Six distinct sample sets of water and sediments were spiked with each benzodiazepine and analyzed. Kd values varied from 1.4 to 9.2 L kg−1 for clonazepam, 1.8–11.5 L kg−1 for alprazolam and 2.31–12 L kg−1 for diazepam. A principal component analysis showed high dependence on Kd with sample characteristics mainly related to sediments. In the systems, whose sediments presented high levels of clay, silt and organic matter, the drugs presented a great interaction with the solid part of the system, increasing the Kd value. Koc values varied from 149.25 to 634.13 L kg−1 for clonazepam, 186.57–852.48 L kg−1 for alprazolam, and 194.68–1189.81 L kg−1 for diazepam. [Display omitted] •Sediment benzodiazepine extraction methods were developed.•Coefficients of partition (Kd) were determined for BDZs in six different systems.•The BDZs studied had different distribution depending to the matrix characteristics.•Clay, silt and organic matter had great influence on Kd values. Capsule: The distribution coefficients (Kd) for bonzodiazepines were evaluated evidencing the interrelation between Kd values, drug and sample characteristics.