Competitive and non-competitive adsorption/desorption of paraquat, diquat and difenzoquat in vineyard-devoted soils.

Mobility of agrochemicals in soils plays an important role in the fate and transport of contaminants in the environment. Competitive and non-competitive sorption experiments of three ammonium quaternary herbicides (paraquat, diquat and difenzoquat) onto eight vineyard soils was measured in batch experiments. Non-competitive experiments show that paraquat (PQ) is the most strongly adsorbed (70-97% of added PQ) followed by diquat (DQ) and difenzoquat (DFQ). The best fits were obtained with the Freundlich equation. In competitive experiments with variable mole ratios, it was found a large influence between the divalent cationic herbicides PQ and DQ, and between them and the monovalent herbicide DFQ, but DFQ did only show a scarce influence on PQ and DQ sorption. Desorption of herbicides into CaCl(2) showed very low values: around 11, 19 and 31% for, respectively, PQ, DQ and DFQ. In order to assess the ability of herbicides to displace others, desorption experiments were carried out by replacing Cl(2)Ca by any of the other two herbicides. In this case, the highest percentage of desorption was obtained when DFQ was desorbed with PQ (>72%) and DQ (>73%), but also when PQ was used to desorb DQ (100%) and vice versa (100%).

Quaternary herbicides retention by the amendment of acid soils with a bentonite-based waste from wineries.

The agronomic utility of a solid waste, waste bentonite (WB), from wine companies was assessed. In this sense, the natural characteristics of the waste were measured, followed by the monitoring of its effects on the adsorption/desorption behaviour of three quaternary herbicides in acid soils after the addition of increasing levels of waste. This was done with the intention of studying the effect of the added organic matter on their adsorption. The high content in C (294 g kg(-1)), N (28 g kg(-1)), P (584 mg kg(-1)) and K (108 g kg(-1)) of WB turned it into an appropriate amendment to increase soil fertility, solving at the same time its disposal. WB also reduced the potential Cu phytotoxicity due to a change in Cu distribution towards less soluble fractions. The adsorption of the herbicides paraquat, diquat and difenzoquat by acid soils amended with different ratios of WB was measured. In all cases, Langmuir equation was fitted to the data. Paraquat (PQ) and diquat (DQ) were adsorbed and retained more strongly than difenzoquat (DFQ) in the acid soil studied. However, the lowest retention of DFQ in an acid soil can be increased by amendment with organic matter through a solid waste from wineries, and it is enough for duplicate retention a dosage rate of 10t/ha. Anyway, detritivores ecology can still be affected. Detritivores are the organisms that consume organic material, and in doing so contribute to decomposition and the recycling of nutrients. The term can also be applied to certain bottom-feeders in wet environments, which play a crucial role in benthic ecosystems, forming essential food chains and participating in the nitrogen cycle.

Influence of organic matter removal on competitive and noncompetitive adsorption of copper and zinc in acid soils.

We studied competitive and noncompetitive adsorption of copper and zinc in four acid soils, and compared the behavior of the two metals in untreated samples and samples treated with hydrogen peroxide to remove organic matter in the soil. Copper exhibited stronger competitive adsorption than zinc in the untreated samples. However, removal of organic matter reduced copper adsorption to a greater extent than zinc adsorption, the two metals exhibiting a more similar adsorption pattern than the untreated samples. The presence of copper dramatically reduced zinc competitive adsorption in untreated samples; on the other hand, that of zinc only resulted in slightly reduced competitive adsorption of copper. The hydrogen peroxide treatment decreased competitive adsorption in both metals; however, copper continued to be more efficient than zinc in competing for binding sites on adsorbing surfaces. Desorption of Cu occurred much less readily than desorption of Zn and hysteresis is apparent especially for Cu.