Effect assessment of reclaimed water and carbamazepine exposure on the thyroid axis of X. laevis: Apical and histological effects

There is increasing environmental concern about the constant presence of pharmaceuticals and personal care products (PPCPs) in surface water, generally attributed to water discharge from wastewater treatment plants (WWTPs) that are unable to completely remove these compounds. The slight, but continuous, presence of these contaminants in reclaimed water (RW) poses a risk of chronic and sublethal toxicity, and the thyroid axis can likely be a target of many of these PPCPs. In this work, we addressed the effects of RW on the Xenopus laevis thyroid system. The Amphibian Metamorphosis Assay (AMA test) was used with modifications by exposing X. laevis tadpoles to RW samples, and to RW spiked with carbamazepine (CBZ) at 100 and 1000 higher than the average levels environmentally relevant (RW 100× and RW 1000×, respectively). Carbamazepine was selected because it is considered a marker of anthropogenic pollution and could have a potential effect on the thyroid axis. The morphological endpoints and histological alterations to the thyroid gland were evaluated. The results suggested the stimulation of the thyroid gland from exposures to the RW samples, supported by tadpoles' accelerated development and by the histological alterations observed in the thyroid gland. Developmental acceleration was also seen in the tadpoles exposed to the RW-100× and -1000× samples at comparable levels to those seen in exposures to RW samples alone. Hence CBZ did not seem to increase the effects of RW on the thyroid axis. Overall, our results suggested endocrine effects of these RW samples regardless of the CBZ concentration.

Sublethal and chronic effects of reclaimed water on aquatic organisms. Looking for relationships between physico-chemical characterisation and toxic effects

The use of reclaimed water for irrigation and aquaculture purposes is generally considered a reliable alternative for sustainable water management in regions with water scarcity. Many organic compounds, generally called compounds of emerging concern (CECs), have been detected in reclaimed water, which implies continuous exposure for aquatic organisms. To date no quality criteria have been proposed for this group of compounds. This work aims to assess the acute, sublethal and chronic effects of reclaimed water using two representative organisms of the aquatic compartment; the green alga Chlorella vulgaris and the microcrustacean Daphnia magna. The study comprises the 72 h-algal growth inhibition test, the D. magna feeding bioassay and the D. magna reproduction test. The results highlighted, for the selected characterised compounds, no differences in the concentrations between the different tertiary WWTP treatments, except for the particular case of carbamazepine. Considering seasonality, no differences were observed between the two different sample collection campaigns. The sublethal and chronic effects observed for these samples could not be explained by the lower concentrations found in the chemical characterisation. However, in the majority of cases, dilution of raw reclaimed water reduced the toxic effects of these samples. Several interactions among compounds can affect the mixture's toxicity. Canonical correlation analyses (CCA) were included to explore the potential relationships between the physico-chemical characterisation of reclaimed water and effects on aquatic organisms. The results corroborated the toxic effect of some pharmaceuticals, in particular beta-blockers and antibiotics, on the growth and yield of green algae, as well as inhibition of daphnia reproduction. Thus the CCA methods could help to elucidate the potential relationships between the physico-chemical characterisation and toxic effects by considering all the potential interactions.