Investigating colloid-associated transport of cadmium and lead in a clayey soil under preferential flow conditions

Colloids have a high adsorption capacity and can be mobile under preferential flow, and so may facilitate heavy metal migration. Heavy metal migration with soil colloids in a clayey soil under preferential flow conditions was investigated through experiments. Adsorption tests were carried out to determine the adsorption of Cd2+ and Pb2+ to the clay and colloids. The preferential flow characteristics in the soil column were investigated by dye tracing tests. The mobility of soil colloids in the soil column was studied by breakthrough tests. Leaching tests of cadmium and lead with and without colloids were carried out conditions. The adsorption tests showed that soil colloids adsorbed more cadmium and lead than the silty clay. The dye tracing tests showed that moderate preferential flow in the soil column can be obtained by choosing clod-size distribution and dry density. The co-leaching test showed that the outflow of cadmium and lead was 1.49 and 33.88 times greater with colloids than without, respectively. The heavy metals adsorbed onto clay and the pore concentrations were both lower with colloids than without, indicating more heavy metals migrated downward with colloids. The migration of cadmium and lead was greatly enhanced by colloids under preferential flow conditions.

Effectiveness of Carbaryl, Carbofuran and Metolachlor Retention in Soils under the Influence of Different Colloid

The affinity of different soil colloids to retain carbaryl, carbofuran and metolachlor in sandy loam and loam soil from mineral, surface horizons was investigated. The undisturbed soil samples and soils amended with colloids—kaolinite (K), montmorillonite (Mt), illite (Il), goethite (G), humic acid (HA)—were mixed with the pesticides for sorption–desorption studies. Their sorption magnitude in pristine soils followed the sequence metolachlor > carbaryl > carbofuran, with loam soil being a better pesticides retarder than sandy soil. The biggest magnitude of carbaryl sorption in light soil was observed in samples with the addition of HA (92.7%), Il (92.3%) and Ge (87.5%), whereas for carbofuran it was goethite (52.3%). Metolachlor uptake was significantly enhanced by 2:1 clays (Mt-85.0%, Il-69.4%), goethite (73.3%) and humic acids (75.4%). The loamy soil sorption capacity of the studied pesticides was blocked by the natural organic matter potentially due to the formation of organo-mineral complexes. HA (66.8%) was the most effective sorbent for carbaryl in the loamy soil, whereas Mt (55.1%) and HA (40.3%) for carbofuran. Metolachlor was retained to the same extent in all loamy soil variants (75.8–83.6%) and its desorption values were the lowest. Carbofuran demonstrated the greatest ability to leach among the studied chemicals.

Retention of the Antibiotic Cefuroxime onto Agricultural and Forest Soils

Antibiotics in wastewater, sewage sludge, manures, and slurries constitute a risk for the environment when spread on soils. This work studies the adsorption and desorption of the antibiotic cefuroxime (CFX) in 23 agricultural and forest soils, using batch-type experiments. Our results show that the adsorption values were between 40.75 and 99.57% in the agricultural soils, while the range was lower (from 74.57 to 93.46%) in forest soils. Among the Freundlich, Langmuir, and Linear models, the Freundlich equation shows the best fit for the adsorption results. In addition, agricultural soils with higher pH are the ones that present the highest adsorption. Further confirmation of the influence of pH on adsorption is given by the fact that Freundlich’s KF parameter and the Linear model Kd parameter shows a positive correlation with pH and with the exchangeable Ca and Mg values, which are known to affect the charges of the soil colloids and the formation of cationic bridges between adsorbents and adsorbate. In addition, Freundlich’s n parameter shows a positive and significant correlation with the organic matter content, related to the high adsorption taking place on forest soils despite their pH < 5. Regarding desorption, in most cases, it is lower than 1%, which indicates that CFX is adsorbed in a rather irreversible way onto these soils. Overall, these results can be considered relevant regarding their potential impact on environmental quality and public health.