Molecular Ecotoxicity Of Volatile Methylsiloxanes In Low Dose

Volatile methylsiloxanes (VMSs) are frequently added to personalcare products (PCPs) and have been released to the environmentcontinuously. With widespread environmental distribution, concernsregarding their risks to environment and human health have been raisedrecently. In this paper,7typical cyclic VMSs (cVMSs) and linear VMSs(lVMSs) were evaluated, including cVMS hexamethylcyclotrisiloxane(D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane(D5) and lVMS hexamethyldisiloxane (L2), octamethyltrisiloxane (L3),decamethyltetrasiloxane (L4), dodecamethylpentasiloxane (L5).Tetrahymena thermophila were used to study the environmental risks bytesting effects of VMSs, especially in environmentally relevant levels, ongrowth, antioxidant system and multixenobiotic resistance (MXR)mechanism. The risks to human health were also evaluated by determiningthe cell viability of human embryonic lung fibroblast (MRC-5). The resultswere as followed.(1) No significant effects were observed on the growth of T.thermophila during60h exposure to cVMS or lVMS in the tested nominalconcentration range as1,5,10,50and100μmol·L-1.(2) As to effects of VMSs on the antioxidant system of T. thermophila,cVMS D3and D4significantly induced SOD activities, while no variationwere observed on CAT activities of cVMS treatment groups. Compared tothe control, lVMS exposure caused significant differences (P<0.05) inSOD activities with L2and L3induced yet L4and L5inhibited SODactivities. Each lVMS exposure resulted in significant inhibition in CATactivities (P<0.05). Combined with SOD/CAT ratio, cVMS D3and lVMS L2, L3significantly affected antioxidant system of T. thermophila inenvironmentally relevant levels. Moreover, the effects on SOD/CAT ratiowere also showed concentration dependent relationship for lVMS L2andL3. In the tested nominal concentration range, there were no significanteffects (P<0.05) on GST activities or GSH contents. The product of lipidperoxidation process MDAcontents were neither showed no change.(3) In the tested nominal concentration range as1,5,10μmol·L-1, nosignificant effects (P<0.05) were found on the MXR mechanisms.However, when VMS combined with MXR inhibitor verapamil as5+5μmol·L-1, activities of MXR transporter increased significantly. Themechanism about the observation still needs further research.(4) VMSs acute exposure resulted in significant effects on the cellviability of MRC-5. In particular, cVMS D3and lVMS L2, L5showedhormesis in the environmentally relevant levels. Overall, the effects ofVMSs on the cell viability displayed no unambiguous trends asconcentration-response relationship.