This study was undertaken to investigate combined toxic and genotoxic effects of cadmium (Cd) and arsenic (As) on white clover, a pollutant sensitive plant frequently used as environmental bioindicator. Plants were exposed to soil spiked with increasing concentrations of cadmium sulfate (20, 40 and 60 mg Kg−1) or sodium arsenite (5, 10 and 20 mg Kg−1) as well as with their combinations. Metal(loid) bioavailability was assessed after soil contamination, whereas plant growth, metal(loid) concentration in plant organs and DNA damage were measured at the end of plant exposition. Results showed that individual and joint toxicity and genotoxicity were related to the concentration of Cd and As measured in plant organs, and that As concentration was the most relevant variable. Joint effects on plant growth were additive or synergistic, whereas joint genotoxic effects were additive or antagonistic. The interaction between Cd and As occurred at both soil and plant level. In soil the presence of As limited the bioavailability of Cd, whereas the presence of Cd increased the bioavailability of As. Nevertheless only As biovailability determined the amount of As absorbed by plants. The amount of Cd absorbed by plant was not linearly correlated with the fraction of bioavailable Cd in soil suggesting the involvement of additional factors, such as plant uptake mechanisms. These results reveal that the simultaneous presence in soil of Cd and As, although producing an additive or synergistic toxic effect on Trifolium repens L. growth, generates a lower DNA damage.

Chaos theory is one of the fields of research that has many practical applications. An important application of chaos in communication is that it can be used for secure communication. To be able to use the chaotic signal in communication, we need to synchronize the chaotic signal between the receiver and the transmitter. In this paper, a sliding mode controller is proposed for global synchronization between two chaotic systems. The interesting point of this controller is that it can help reduce the synchronization time based on the selection of the appropriate gain parameter. This method has also been applied to a secure communication system with chaos masking. Finally, numerical simulations are given to illustrate the effectiveness of the proposed method.

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