The occurrence and wastewater chlorination fate of selected pharmaceuticals in South African surface water

Abstract

The world’s water is a rapidly deteriorating and declining resource, which stands to negatively impact every nation on earth. Recently, it has been noted that pharmaceuticals and their disinfection transformation products are present in water supplies. These compounds as well as endocrine disruptors and personal care products are collectively known as micropollutants. Water quality is of special interest to the defence community and as a result the South African National Defence Force initiated this work, to be carried out at Protechnik Laboratories, a division of ARMSCOR SOC Ltd. The major aims of this research are concerned with the detection and quantification of micropollutants, specifically pharmaceuticals relevant to South African society, in surface water on a national scale; and how these compounds change as a result of wastewater chlorination. The differences between the original parent compound and the disinfection transformation products’ in vitro toxicity and activity are also addressed. The thesis is divided into separate publications, each with its own topic, yet they are all bound in that they serve to describe particular themes: how mass spectrometry has evolved to answer environmental chemistry questions and how the interface between chemistry and biology, as well as an understanding of each effectively serves to answer some of the most difficult scientific questions. Very little work regarding the detection and quantification of antiretroviral compounds (ARVs) has been described in the literature; most likely due to the regional prevalence of human immunodeficiency virus (HIV). A novel method for the simultaneous quantification of 12 ARVs using the standard addition method was developed. South African surface water, from across the country was concentrated by solid phase extraction (SPE) and analysed by liquid chromatography coupled to a triple quadrupole tandem mass spectrometer (LCMS/ MS). Matrix effect was found to substantially affect sample quantitation with an average corrected method detection limit of 90.4 ng/L. This is the first report of a countrywide survey of South African surface water for the quantification ARVs with average concentrations ranging between 26.5 and 430 ng/L. Using a broader approach, liquid chromatography coupled to quadrupole time of flight mass spectrometry (LC-QTOF) was utilised to quantify 99 pharmaceuticals in SPE extracts of South African surface water on a national level. In addition to this, a non-targeted approach was developed in which three commercially available mass spectral databases, combined into a single searchable entity and parallelized by cluster computing were utilised to screen water samples. This broad approach was combined with automatically triggered tandem mass spectrometry to yield fragmentation data for unknown compounds; for database comparison. Limits of quantification were in the low ng/L range for the majority of the compounds and it was found that nationally both Lamotrigine and Nevirapine occurred most often. Prednisolone and Ritonavir were present at the highest average concentration; 623 and 489 ng/L respectively. It is noteworthy that more than 50% of the targets chosen for analysis are not detectable in any of the samples, which highlights the utility of untargeted, database driven screening; prior to the use of costly analytical standards. The untargeted approach, which was stringent, detected 45 % of the compounds found in targeted mode, and furthermore tentatively identified a total of 4273 unique compounds across the samples. Automatic tandem mass spectrometry yielded 92 unique hits with greater than 95 % confidence. From these results it is clear that untargeted screening should precede the targeted approach as a matter of economy and to guide the selection of targets for quantification. There is still room for improvement in the field as the computational analysis of the large data sets created in this research represents a substantial bottleneck in the analytical workflow. The wastewater disinfection process, in addition to releasing pharmaceuticals into the environment, has been found to lead to the transformation of these compounds; resulting in the formation of a variety of undescribed disinfection transformation products (DTPs). The biological activity and toxicity of these DTPs are largely unknown. We investigated the laboratory scale chlorination of the commonly used anti-HIV drug Nevirapine, which occurs ubiquitously in surface water, as shown by our earlier research. The chlorination kinetics of the compound was determined under realistic wastewater treatment concentrations and by scaling up the chlorination reactions the various DTPs were characterised by LCQTOF. DTPs were produced, isolated by preparative chromatography and subjected to in vitro toxicity and antiviral activity analyses.