Does the natural carcinogen ptaquiloside degrade readily in groundwater?

Abstract

Background Ptaquiloside (PTA) is a natural carcinogen found in bracken ferns. PTA is released from the plants via soil to surface and groundwaters from where humans can be exposed via drinking water. Primary degradation of PTA is due to hydrolysis with formation of pterosin B (PTB). Temperature and pH determine the rate of hydrolysis under pure experimental conditions. To assess the applicability of the experimental model to natural groundwaters, PTA degradation kinetics were examined in a range of natural groundwaters at environmentally relevant conditions. Results PTA was quantified by UPLC-MS/MS. Over an 80-day study period, PTA half-lives ranged from 6.5 to 47 days (natural pH; 8.0 °C). The fastest degradation was observed for the most alkaline groundwaters with pH of around 8. Rates of degradation were well predicted using an existing mathematical model for hydrolysis. However, deviations from this model were found, especially at the extremes of the examined pH-range (4.7–8.2). The degree of conversion of PTA to PTB was close to unity around neutral pH. However, at slightly acidic conditions, formation of PTB could only count for 9% of the degraded PTA, indicating formation of other products. Conclusions Degradation of PTA in groundwater is determined by pH and temperature, and PTA can prevail for months under slightly acid to neutral pH conditions. The existing laboratory-based model for PTA hydrolysis is generally applicable for groundwaters but needs further validation at high and low pH.

Removal of phytotoxins in filter sand used for drinking water treatment

“…The observed rate constants are faster than the predicted rates by about two orders of magnitude. Our results suggest that the existing model ( Wu et al, 2021 ) based on pH and temperature and relevant for hydrolysis in groundwater, does not capture all relevant dynamics in rapid sand filters at waterworks that also contain solids.…”

“…Ptaquiloside can undergo acid as well as alkaline hydrolysis and the rate of hydrolysis is strongly pH dependant ( Ayala-Luis et. al., 2006 ; Wu et al, 2021 ). Ptaquiloside, as well as the main product of hydrolysis (pterosin B), can be microbially degraded under environmental conditions in soils ( Skourti-Stathaki et al, 2016 ).…”

Occurrence and stability of ptesculentoside, caudatoside and ptaquiloside in surface waters

“…Sterilisation could not explain the overall faster degradation rates in experiments in F and H. The general applicability of eqn (1) to describe PTA hydrolysis in waters of different origin is also in line with studies of PTA hydrolysis in groundwater. 42 However, in presence of solids, eqn (1) may not be valid. Hence, PTA degradation in sand filters was found to be two orders of magnitude faster than predicted by eqn (1).…”

“…In natural waters and soils, PTA degradation can be accelerated by microbial activity and decelerated by organic matter content. 28,41,42 Also, the presence of clay silicates may slow down PTA degradation, possibly through sorption. 28 Therefore, factors not included in eqn (1) may increase or decrease the rate of PTA degradation in natural waters compared with predictions made by the equation.…”

Natural toxins: environmental contaminants calling for attention

“…Wu et al [54] compared the stability of ptaquiloside in natural groundwater under environmentally relevant conditions with laboratory-based models and found a good agreement under slightly acid to neutral pH. Under such conditions, ptaquiloside was found to prevail for months.…”