Copper distribution in water-dispersible colloids of swine manure and its transport through quartz sand

To demonstrate the potential risks associated with the application of solid agricultural wastes, we investigated Cu distribution in water-dispersible colloids derived from swine manure and its transport through quartz sand. Samples were sequentially centrifuged to obtain five colloid suspensions (<10, <1, <0.45, <0.2, and <0.02 μm) and four colloid subsamples (1-10, 0.45-1, 0.2-0.45, and 0.02-0.2 μm). We observed that 2% of Cu in the swine manure was found in the 0.02-10 μm colloid fractions, while 18% was observed in the <0.02 μm colloid suspension. The highest accumulation of Cu was found in the 0.02-0.2 μm fraction of colloids, in which organic carbon was the major component. The Cu in the 1-10 μm colloid fraction existed in both inorganic compounds and organic associations, whereas it mainly existed as organic complexes in colloids <1 μm (<0.53 μm, specifically). Furthermore, large colloids (1-10 μm) of swine manure were partially filtered out as they passed through the sand particles, and fine colloids facilitated the transport of Cu. The formation of organic complexes was hypothesized to enhance the mobility of Cu. Further research is needed to incorporate our experimental findings into a realistic model of particle mobilization and transport through soil or groundwater aquifers.