Deconjugation potentials of natural estrogen conjugates in sewage and wastewater treatment plant: New insights from model prediction and on-site investigations

Natural estrogen conjugates play important roles in municipal wastewater treatment plant (WWTP), but their deconjugation potentials are poorly understood. This work is the first to investigate the relationships between the enzyme activities of arylsulfatase/β-glucuronidase and deconjugation potentials of natural estrogen conjugates. This work led to three important findings. First, the enzyme activity of β-glucuronidase in sewage is far higher than that of arylsulfatase, while their corresponding activities in activated sludge were similar. Second, a model based on β-glucuronidase could successfully predict the deconjugation potentials of natural estrogen glucuronide conjugates in sewage. Third, the enzyme activity of arylsulfatase in sewage was too low to lead to evident deconjugation of sulfate conjugates, which means that the deconjugation rate of estrogen sulfates can be regarded as zero. By comparing their theoretical removal based on enzyme activity and on-site investigation, it is reasonable to conclude that reverse deconjugation of estrogen conjugates (i.e., conjugation of natural estrogens to form conjugated estrogens) likely exist in WWTP, which explains well why natural estrogen conjugates cannot be effectively removed in WWTP. Meanwhile, this work provides new insights how to improve the removal performance of WWTP on natural estrogen conjugates. SYNOPSIS: This work is the first to show how arylsulfatase/β-glucuronidase could affect deconjugation of natural estrogen conjugates and possible way to enhance their removal in wastewater treatment plant.

Stability properties of natural estrogen conjugates in different aqueous samples at room temperature and tips for sample storage

It is important to keep natural estrogen conjugates (C-NEs) intact in aqueous environmental sample before sample preparation; otherwise, this may influence the accurate determination of NEs. Therefore, this work thoroughly investigated the stability of C-NEs in three different aqueous environmental samples under four different storage conditions, room temperature, low temperature of 4 °C, low pH of 3, and addition of HgCl₂ at 2 g/L. Results showed that C-NEs in aqueous sample were easily deconjugated under low temperature of 4 °C, which has been widely used in sample collection and storage. Both the low pH of 3 and addition of HgCl₂ at 2 g/L under room temperature could keep C-NEs intact in domestic wastewaters and river water within 36 h, but the latter could keep C-NEs stable longer. This work is the first to show that low pH of 3 alone could keep C-NEs intact, which suggested that the combined condition at low temperature of 4 °C that has been widely used could be omitted. Meanwhile, compared to pH adjustment, addition of 2 g/L HgCl₂ into aqueous sample is more convenient and practical for 24-h composite sampling, which may be widely applied.