Adsorption of sulfamethoxazole and ethofumesate in biochar- and organoclay-amended soil: Changes with adsorbent aging in the laboratory and in the field

• Published in: The Science of the total environment 2024-08, Vol.939, p.173501, Article 173501
• Main Authors: López-Cabeza, Rocío, Cox, Lucía, Gámiz, Beatriz, Galán-Pérez, Jose Antonio, Celis, Rafael
• Format: Article
• Language: English
• Subjects: Adsorption; Aging; Agrochemical; Biochar; Charcoal - chemistry; Clay - chemistry; Organoclay; Soil; Soil - chemistry; Soil Pollutants - analysis; Soil Pollutants - chemistry; Sulfamethoxazole - chemistry
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2024.173501

Biochars and organoclays have been proposed as efficient adsorbents to reduce the mobility of agrochemicals in soils. However, following their application to soils, these adsorbents undergo changes in their physicochemical properties over time due to their interaction with soil components. In this study, the adsorption capacity of a commercial biochar and a commercial organoclay for the antibiotic sulfamethoxazole (SFMX) and the pesticide ethofumesate (ETFM) was evaluated over aging periods of 3 months in the laboratory and 1 year in the field, subsequent to their application to a Mediterranean soil. The results showed that the adsorption of SFMX and ETFM in the soil amended with the adsorbents was greater than in the unamended soil, but for both chemicals, adsorption decreased with aging of the adsorbents in the soil. Characterization of the adsorbents before and after aging revealed physical blocking of adsorption sites by soil components. The loss of adsorption capacity of the adsorbents upon aging led to higher leaching of SFMX and ETFM in the soil containing field-aged adsorbents, although leaching remained lower than in unamended soil. Our findings reveal that, under the Mediterranean environment studied, the efficacy of the studied materials as adsorbents is maintained to a considerable extent for at least one year after their field application, which would have positive implications in their use for attenuating the dispersion of agricultural contaminants in the environment. [Display omitted] •Sulfamethoxazole (SFMX) and ethofumesate (ETFM) adsorption to soil was low.•Soil amendment with biochar and organoclay increased adsorption of SFMX and ETFM.•The adsorption of SFMX and ETFM decreased with aging of the adsorbents in the soil.•Leaching of SFMX and ETFM through the soil increased with adsorbent aging.•The efficacy of the adsorbents in reducing leaching remained high after one year.