| dc.description.abstract | Dumping of illicit drug production waste, namely amphetamine-type substances (ATS), is an issue that Dutch authorities continually grapple with due to the concentrated production of such drugs in the Netherlands. This production waste is often discovered by happenstance, having been haphazardly and surreptitiously dumped into nature preserves or near surface water bodies. In the former case, drug waste containers may occasionally leak into the soil, potentially discharging high concentrations of ATS chemicals into the subsurface and posing a threat to groundwater contamination. This thesis set out to perform an array of soil sorption experiments that would provide empirical data that enhances the understanding of how these chemicals behave in the soil system.
Sorption experiments were performed using a soil sample collected from the subsurface of the Utrechtse Heuvelrug, where the sampling location lie within 50 meters of a municipal drinking water well. A sorption methodology conducted on five ATS chemicals—MDMA, methamphetamine, APAAN, BMK, and safrole—at spike concentrations of 300, 150, 75, 37.5, 18.75, 9.38, 4.69, 2.35, and 1.17 μg/L provided the necessary data to develop sorption isotherms. 15 mL Cellstar® tubes containing a soil mass to spike solution ratio of 2 grams to 4 mL, performed in triplicate at each concentration, were laid flat and mixed for 48 hours in an orbital shaker operating at 130 rpm. Sample vials were then centrifuged at 3000 Gs for 30 minutes, after which the supernatant solutions passed through 0.20 μm Phenomenex syringe filters into 1.8 mL amber LCMS-safe analysis vials.
LCMS sample analysis using an Vanquish LC pump and an Orbitrap Fusion provided equilibrium aqueous phase concentrations, Ce, which were then used to calculate the concentration of each test chemical sorbed to the soil phase, Cd. These values provided the necessary data to construct sorption isotherms that describe the sorption behavior of each compound in the soil sample. Experimental data indicate that the sorption of MDMA, methamphetamine, and APAAN are adequately described by the Freundlich model, as they exhibit nonlinear sorption with increasing equilibrium aqueous concentration. MDMA, methamphetamine, and APAAN Freundlich equations had 1/n values of 0.9046, 0.8415, and 0.5994, respectively, falling below the upper end of the nonlinear threshold value of 1/n=1. Freundlich coefficient values, KF, were 24.29 for MDMA, 7.51 for methamphetamine, and 207.1 for APAAN, demonstrating that these compounds exhibit notable sorption to the soil sample. Comparison of organic carbon normalized sorption values, logKFOC, of MDMA and methamphetamine to those of Pal et al. (2008) suggest that these sorption coefficients adequately describe the behavior of these chemicals in the soil (Pal et al., 2008). Data for BMK was insufficient for calculation of a Freundlich coefficient, but does show that sorption of BMK is orders of magnitude lower than it is for MDMA, methamphetamine, and APAAN. No data for safrole was available for analysis due to detection issues in the LCMS.
These experimental data indicate that sorption of ATS chemicals is variable depending on the individual compound and its chemical structure. MDMA and methamphetamine, based on the isotherm data and comparisons to literature, are likely to degrade in the soil before they would pose a threat to infiltration into the groundwater. APAAN had no degradation information available at the time of this research, but its high sorption affinity to the soil suggests that it will remain in the soil. Drawing definitive conclusions on environmental fate of BMK and safrole is not possible given the incomplete nature of their data. Altogether, this thesis provides empirically determined soil sorption values that are useful in expanding the understanding of ATS drug chemicals in Dutch soil. | |
