Ozonation products of purine derivatives, the basic structures of antiviral micropollutants.

Purine and its nucleobases adenine and guanine are the basic structures of a large group of antiviral agents such as acyclovir and penciclovir. Hence, their ozonation is of interest with regard to wastewater treatment due to the formation of products that could affect the aquatic environment. In this study, the transformation products of the mentioned substances are investigated under different defined reaction conditions in order to gain insight into the ozonation characteristics of this compound class. Results show that examining related molecules significantly improves product screening by compiling known products and analogues leading to comprehensive candidate lists, for the purines with a total number of >120 candidates (including possible duplicates for several purines) of which 49 were detected for the derivatives studied. One product, cyanuric acid, which was previously postulated for adenine, was tentatively confirmed and quantified for the first time for the reaction of purine and adenine with ozone. In addition, two prioritisation approaches are presented to identify the major products that are either formed under specific reaction conditions or are potentially relevant for structurally related pollutants. First, principal component analysis allowed the prioritisation of the products formed according to reaction conditions. In the analysis of guanine and the two antivirals, this approach showed that at neutral and basic pH the 2-imino-5-oxoimidazoline products dominated while at acidic pH either analogues of 5-amino-2,4-imidazolidinedione or 2,4-diamino-1,3-oxazol-5-(2H)-one were abundant. A second approach prioritising common products in the ozonation of all three basic structures revealed the formation of two products that had not been reported before: C4H8O3 and C3H2N2O3, presumably oxalylurea. Both molecules or their analogues may also be formed from related micropollutants. Overall, examining basic structures and exemplary micropollutants in combination was shown to be a worthwhile approach to gain knowledge on the ozonation of a whole range of compounds.

Elucidating nicotine transfer into water environments via cigarette butt remaining parts.

Nicotine, the main alkaloid in tobacco, enters water environments through discarded cigarette butts (CBs), possibly causing detrimental effects. However, there is no comprehensive investigation on the long-term leaching of nicotine from the different CBs parts. Therefore, in the present study, the ecological risk and the leachate levels of nicotine from different CBs parts were investigated. Freshly smoked CBs, aged CBs collected from streets, remaining tobacco and ash of freshly smoked CBs, and filter plus paper of freshly smoked CBs were evaluated for the leachate experiments. The order of nicotine leachate from different types of CBs and parts investigated were as remaining tobacco plus ash of freshly smoked CBs > freshly smoked CBs > aged CBs > filter plus paper of freshly smoked CBs with the ranges of 5.73-17.34, 0.36-8.6, 0.31-4.12, and 0.17-2.79 mg of nicotine per g of CB or remaining parts (mg g-1), respectively. The ecological risk assessment revealed that nicotine leachates from all the CBs types or their remaining parts could be highly hazardous to fish, cladocerans, algae, and Daphnia magna. Based on the mean leachate levels of nicotine via freshly smoked CBs at exposure times of 1 min to 1 month and the estimated number of littered CBs every year on a worldwide scale, freshly smoked CBs may release 380-7065 tons of nicotine into water environments.

Effects of organic matter and alkalinity on the ozonation of antiviral purine derivatives as exemplary micropollutant motif.

Ozonation of micropollutants strongly depends on the water matrix. Natural organic matter is known to highly affect the hydroxyl radical exposure due to radical promoting and inhibiting effects. Other important matrix components in ozonation are carbonate species which scavenge hydroxyl radicals. However, additional factors such as the formation of other radicals might also play a role but are generally not covered in research or considered in modelling of micropollutant degradation. Hence, the ozonation of purine derivatives, the basic structure of various antiviral micropollutants, in different artificial water matrices is investigated in this study with focus on the impact of natural organic matter and increasing alkalinity on the degradation and product formation. The degradation of purine and adenine is inhibited by bicarbonate in the water matrix due to the anion's scavenging of hydroxyl radicals. This effect is already observed for low bicarbonate concentrations of 0.3 mM. However, formed carbonate radicals contribute to the compounds' degradation and also affect the stability of transformation products. This effect gains in relevance with increasing alkalinity and needs consideration in evaluating ozonation of very hard waters. Three ozonation products are evaluated in detail, which are affected by the matrix due to impacts on ozone stability, hydroxyl radical yield and carbonate radical formation. One product of adenine with the mass 147 was reported for the first time and only occurs in presence of matrix components. Under typical water treatment conditions rough predictions of pollutants' degradation are possible by the Rct concept using ozone and hydroxyl radical exposures. However, other reactive species such as carbonate radicals are not considered leading to deviations between modelled and experimental data at extreme conditions such as industrial wastewater. A general correlation between the Rct and the fraction f of hydroxyl radicals scavenged by bicarbonate (ln(Rct) = - 5.9  ×  f - 16.3) calculated from the concentration of organic matter and alkalinity was observed for various water samples allowing the estimation of micropollutant degradation during ozone treatment at moderate conditions by simple organic and inorganic carbon measurements.