Vitellogenin gene expression in marine mussels exposed to ethinylestradiol: No induction at the transcriptional level

Comparative toxicity of urban wastewater and rainfall overflow in caged freshwater mussel Elliptio complanata

Municipal effluents are well-recognized as disrupting sexual differentiation and reproduction in mussels. However, the contribution to this problem made by rainfall combined with sewer overflow (increased by rain due to climate change) is not well understood. The purpose of this study was to compare the neuroendocrine effects of municipal discharge and rainfall overflow on caged endemic mussel Elliptio complanata. To this end, mussels were experimentally caged and placed for 3 months at a municipal effluent dispersion plume site and at overflow sites. Data revealed that downstream surface water contained some pharmaceuticals (caffeine and carbamazepine) and accumulated significant levels of heterotrophic bacteria, but these effects were not observed at the overflow sites. The principal effects observed at the downstream site were increased soft tissue mass (and gonad index), inflammation, and Vtg proteins in male mussels as determined by a novel immunostaining methodology. The rainfall overflow sites had no effects on these markers, but were specifically associated with reduced Vtg proteins in females, dopamine (Dop), gonad lipids, and DNA strand breaks, with increased metallothioneins. In conclusion, the observed feminizing effects of municipal effluent were not additionally observed in mussels caged at rainfall overflow sites, although the latter exhibited a different pattern of toxicity.

Gene expression and biochemical patterns in the digestive gland of the mussel Mytilus galloprovincialis (Lamarck, 1819) exposed to 17α-ethinylestradiol

Contaminants of emerging concern (CECs) are a class of chemicals that can spread throughout the environment and may cause adverse biological and ecological effects. While there are many different classes of CECs, one of the most well documented in the aquatic environment are pharmaceutical drugs, such as natural and synthetic estrogens. In particular, the widespread presence of the synthetic estrogen 17 α-Ethinylestradiol (EE2) in water may lead to bioaccumulation in sediment and biota. EE2 is the primary component in contraceptive pills, and is a derivative of the natural hormone estradiol (E2). In this study, the mussel Mytilus galloprovincialis was exposed to EE2 in a semi-static and time-dependent experiment, for a total exposure period of 28 days. Biochemical and transcriptomics analyses were performed on mussel digestive glands after exposure for 14 (T14) and 28 (T28) days. Metabolic and DNA impairments, as well as activation of antioxidant and biotransformation enzymes activation, were detected in T28 exposed mussels. RNA-Seq analysis showed significant differential expression of 160 (T14 compared to controls), 33 (T28 compared to controls) and 79 (T14 compared to T28) genes. Signs of stress after EE2 treatment included up-regulation of gene/proteins involved with immune function, lipid transport, and metabolic and antibacterial properties. This study elucidates the underlying mechanisms of EE2 in a filter feeding organisms to elucidate the effects of this human pharmaceutical on aquatic biota.

The Uptake of Ethinyl-Estradiol and Cortisol From Water by Mussels (Mytilus spp.)

Previous toxicokinetic studies have shown that mussels (Mytilus spp.) can readily absorb the three main mammalian sex steroids, estradiol (E₂), testosterone (T) and progesterone (P) from water. They also have a strong ability to store E₂ and the 5α-reduced metabolites of T and P in the form of fatty acid esters. These esters were shown to have half-lives that were measured in weeks (i.e. they were not subject to fast depuration). The present study looked at the toxicokinetic profile of two other common steroids that are found in water, the potent synthetic oestrogen, (ethinyl-estradiol) (EE_2; one of the two components of 'the pill'), and cortisol, a natural stress steroid in vertebrates. In the first three hours of uptake, tritiated EE₂ was found to be taken up at a similar rate to tritiated E₂. However, the levels in the water plateaued sooner than E₂. The ability of the animals to both esterify and sulphate EE₂ was found to be much lower than E₂, but nevertheless did still take place. After 24 h of exposure, the majority of radiolabelled EE₂ in the animals was present in the form of free steroid, contrary to E_2, which was esterified. This metabolism was reflected in a much lower half-life (of only 15 h for EE₂ in the mussels as opposed to 8 days for E₂ and >10 days for T and P). Intriguingly, hardly any cortisol (in fact none at all in one of the experiments) was absorbed by the mussels. The implications of this finding in both toxicokinetic profiling and evolutionary significance (why cortisol might have evolved as a stress steroid in bony fishes) are discussed.