Time-dependent disturbances of chloride salts on overall redox reaction and luminescence in Vibrio fischeri

Joint action of binary mixtures based on parameter k·ECx from concentration-response curves in long-term toxicity assay

A previous acute toxicity study of binary mixtures showed that the combined toxicity can be predicted with the parameter k∙EC_x. To systematically investigate the ability of k∙EC_x to predict the chronic combined toxicity of binary mixtures, the toxicity of six contaminants and five binary mixtures was determined by long-term microplate toxicity analysis (L-MTA) using Aliivibrio fischeri as the test organism. The independent action model (IA) and the relative model deviation ratio (rMDR) were employed to determine the relationship between the Δ(k∙EC_x)% and rMDR_x. The results showed that these two factors conformed to the exponential function in long-term toxicity. Owing to the time-dependence of toxicity, the mixture type of chronic toxicity changes to the relative type of acute toxicity. If the acute toxicity of binary mixtures changes their mode of joint action throughout the concentration range, the chronic toxicity will also change their mode of joint action, and vice versa. This study clarified the change rules of the joint action of binary mixtures in acute and chronic toxicity which can promote research on chronic toxicity of binary mixtures.

Prediction on the combined toxicities of stimulation-only and inhibition-only contaminants using improved inverse distance weighted interpolation

The evaluation of ecological risks of contaminant mixtures to organisms is very challenging due to the non-linear response of organisms to each component, especially under the co-existence of both stimulators and inhibitors. Whether the stimulatory effect can reduce or even offset the inhibitory effect would be critical to the risk assessment and the treatment measures of mixed pollutants. Here, the combined toxicity of sodium fluoride (NaF), a stimulator with stimulation rate >100%, and six compounds that cannot induce hormesis (four ionic liquids (ILs) and two pesticides) were studied. The time-dependent toxicity of each toxicant on Vibrio qinghaiensis sp.-Q67 was investigated at 0.25, 2, 4, 6, 8, 10 and 12 h. Results showed that four ILs and two pesticides failed to induce hormesis, while NaF induced hormesis from 2 to 6 h and induced stimulation only after 6 h and reached its maximum (650%) at 12 h. All mixture rays with NaF induced hormesis at different times. In the four NaF-IL mixture systems, the absolute value of maximum stimulation demonstrated an upwards and then a downwards trend with the increasing of mixture ratio of IL. In two NaF-pesticide systems, the maximum stimulation effect declined with the increasing of the mixture ratio of pesticide. The toxicities of the mixture were successfully predicted by the improved inverse distance weighted interpolation, which are not able to be predicted by the commonly used concentration addition or independent action models. This paper shed lights on evaluating the hormesis of mixtures and the ecological risk of fluoride.

Alteration in concentration-response curves of four N-alkylpyridinium chloride by exposure concentration, time and in their mixtures by uniform design

The concentration-response curves (CRCs) of chemicals are important in extrapolating their effects from laboratory studies to their risk assessment in the field. Yet, the CRCs can be altered by exposure concentration and mixture conditions, and also by exposure time in recent reports. Presently, ionic liquids (N-alkylpyridinium chloride, [apyr]Cl) were used for CRC-alteration studies. In individual effects on Vibrio qinghaiensis sp. Q67 (Q67) from 0.25 to 24 h, the CRCs of [epyr]Cl and [bpyr]Cl changed from S- to J-shaped with decreases in inhibition and increases in stimulation, while the CRCs of [hpyr]Cl changed from S- to flat-shape with decreases in inhibition but without stimulation. In mixture effects on Q67, the CRCs all changed from S- to J-shaped from 0.25 to 24 h. By means of the variable selection and modeling method based on the prediction (VSMP), the CRC-alterations of mixtures were positively contributed by [epyr]Cl but negatively contributed by [bpyr]Cl. Furthermore, a parameter was developed by the area of a triangular that combined acute inhibition (EC_50,0.25h) and chronic stimulation (Zero-effect Point, i.e., ZEP_24h and the minimum inhibition effect, i.e., E_min,24h). This parameter successfully evaluated the CRC-alterations in both individual and mixture effects over time, and indicated potential interactions in CRC-alteration in mixtures.