Effect of irrigation water type and other environmental parameters on CeO2 nanopesticide-clay colloid interactions
In this work, the stability and aggregation behaviour of CeO2 nanoparticles (NPs) was investigated to predict its fate in the agricultural environment. For that aggregation kinetics of CeO2 NPs was studied under varying pH, ionic strength (IS), dissolved organic matter (DOM) and carbonate concentrations in the presence of clay. Further, a different type of irrigation waters has been used to check the fate of CeO2 naoparticles (NPs) in complex aqueous matrices. Results show that critical coagulation concentration (CCC) values obtained for CeO2 NPs, i.e. 26.5 mM and 7.9 mM for NaCl and CaCl2 respectively, drastically decreased to 16.2 mM and 1.87 mM in the presence of bentonite clay colloids, which may lead to their deposition within the soil matrix. However, the presence of bicarbonate ions (0.1-2 mM) along with DOM (1-20 mg/L) may result in their stabilization and co-transport of CeO2 NPs with clays in water bodies having low ionic strength. It was also observed that the negative charge of bentonite clay suspension was completely reversed with an increase in CeO2 concentration by 37.5 times. The critical charge reversal concentration value was 284.4 mg/L in milli-Q whereas values were observed to be 680 mg/L in synthetic-soft water (SW), followed by natural river water (NW, 867 mg/L) and synthetic-hard water (HW, 910 mg/L). The synergistic effect of temperature and ionic strength was observed on the aggregation behaviour of CeO2 NPs in environmental water samples of varying composition.