Removal of carbamazepine from aqueous solution by adsorption on fly ash-amended soil.

Carbamazepine (CBZ), nonbiodegradable pharmaceutical residue, has become an emerging pollutant in several aquatic environments. The effectiveness of the mixture of soil and fly ash (FA) in adsorbing CBZ from aqueous solution has been studied as well as agitation time, FA content, initial CBZ concentration and desorption as a function of FA content. The adsorption kinetics fits a hyperbolic or pseudo-second-order model. The maximum adsorbed amounts for natural soil and a mixture of soil/FA ranged from 77 to 158 mg kg(-1). Rate constants were considered relatively low (4.15-15.59 × 10(-4) kg mg(-1) min). The logarithmic form of the Freundlich equation gave a linearity and the Kf constants increased with the increase of FA content in adsorbent mixtures and with the affinity between the adsorbent surface and adsorbed solute. The mean removed amounts of CBZ by adsorption batch experiments in a soil mixture with 30% FA content were up to 92.8% for coal FA and 33% in natural soil. This work proved that the mixture of the coal FA and soil can be used as an efficient adsorbent material for removal of CBZ from water.

Comparison of linuron degradation in the presence of pesticide mixtures in soil under laboratory conditions.

It is widely recognised that complex interactions occur between chemicals in mixtures. In many agricultural situations, the use of tank mixes and complex spray programs is a common practice. Insecticides, fungicides and a herbicide being applied in potato protection were used in this research. Interactions between linuron and insecticides, such as thiamethoxam or clothianidin, and fungicides, such as mancozeb or chlorothalonil, were examined in soil. The degradation rate of linuron in soil during laboratory incubation in six treatments was studied. Mixtures of linuron with mancozeb in sandy loam and clay loam soils had a significant effect on the persistence of this herbicide. For example, for the same herbicide, t 1/2 values for linuron were from 37 days in sandy loam to 44 days in clay loam. These values changed (64-67 days) when thiamethoxam and mancozeb were in soil. When mancozeb was added only, the half-life values were from 59 to 62 days, respectively. Other mixtures with chlorothalonil, thiamethoxam and clothianidin did not have any effect. In order to compare linuron degradation rates in soils, a single first-order model and expanded statistical analysis were used.

Atrazine degradation in soil: effects of adjuvants and a comparison of three mathematical models.

BACKGROUND: There are few reports on the effects of spray adjuvants on pesticide persistence. The role of three adjuvants used with atrazine on the herbicide's degradation in soil was examined. Three mathematical models were used to describe pesticide disappearance from soil: pseudo-first-order kinetics, the non-linear Gustafson-Holden model and the biexponential function. RESULTS: A mixture of atrazine with Atpolan 80 EC significantly inhibited herbicide soil degradation (DT50 = 78 days), while Adpros 85 SL and Break-Thru S 240 (DT50 = 25 and 24 days respectively) had little effect (DT50 = 22 days, atrazine alone). These results suggest that adjuvant can be a factor in field persistence. DT50 values obtained using the Gustafson-Holden and biexponential models were similar. Only the biexponential model requires an iterative method. CONCLUSION: A significant effect of one adjuvant on atrazine persistence in soil was observed. The biexponential model best described the disappearance of atrazine in the soil, as indicated by the values of R(2) and RMS and the relative concentration of the herbicide in the soil.

The effects of pesticide mixtures on degradation of pendimethalin in soils.

Most agronomic situations involve a sequence of herbicide, fungicide, and insecticide application. On the other hand, use of pesticidal combinations has become a standard practice in the production of many agricultural crops. One of the most important processes influencing the behavior of a pesticide in the environment is its degradation in soil. It is known that due to several pesticide applications in one vegetation season, the pesticide may be present in mixtures with other pesticides or xenobiotics in soil. This study examines the role which a mixture of chemicals plays in pesticide degradation. The influence of other pesticides on the rate of pendimethalin (PDM) degradation in soil was measured in controlled conditions. Mixtures of PDM with mancozeb or mancozeb and thiamethoxam significantly influenced the degradation of pendimethalin under controlled conditions. The second type of mixtures, with metribuzin or thiamethoxam, did not affect the behavior of pendimethalin in soil. Also, we determined the influence of water content on the rate of pendimethalin degradation alone in two soils and compared it to the rate in three pesticide mixtures. We compared two equations to evaluate the predictors of the rate of herbicide dissipation in soil: the first-order kinetic and the non-linear empirical models. We used the non-linear empirical model assuming that the degradation rate of a herbicide in soil is proportional to the difference of the observed concentration of herbicide in soil at time and concentration of herbicide in the last day of measurement.