Heavy metals, veterinary antibiotics and microplastics in agroecosystems: Occurrence, co-contamination and remediation approaches: A comprehensive review

Abstract

Agroecosystems increasingly face complex mixtures of pollutants from diffuse agricultural and peri-urban sources, collectively termed emerging contaminants (ECs), which remain bioactive at trace levels, are poorly regulated and can act as vectors for co-occurring pollutants. This review synthesises the occurrence, fate, toxicity and remediation of heavy metals (HMs), veterinary antibiotics (VAs) and microplastics (MPs, inclusive of nanoplastics (NPs)) in agroecosystems, with emphasis on India, where intensive livestock-crop integration, weak wastewater treatment and high mulch-film use favour co-contamination. Heavy metal through classical rather than emerging pollutants, are included given their sorption and complexation interactions with VAs and MPs. In Indian farmlands, cadmium (Cd), lead (Pb), chromium (Cr), arsenic (As) and nickel (Ni) concentrations span roughly two orders of magnitude and frequently exceed World Health Organization/Food and Agriculture Organization (WHO/FAO) limits in industrial and intensively cropped zones. Veterinary antibiotic residues in manure-amended soils range from sub-µg kg-1 to several hundred µg kg-1 (tetracyclines, fluoroquinolones, sulfonamides dominant), while MP abundance ranges from ~ 50 to > 1000 particles kg-1, chiefly polyethylene and polypropylene. Microplastics and metals (Pb, Cd, Cr) can act as sorption/complexation partners for antibiotics, enhancing their persistence and mobility, though mechanisms remain incompletely characterised. Co-contamination degrades soil quality, disrupts microbial communities, co-selects resistance genes, suppresses crop productivity and raises human exposure via food and dust. Remediation studies report 60–90 % Cd/Pb immobilisation (biochar-zeolite), 60–94 % ciprofloxacin removal (vetiver grass), 99 % sulfamethoxazole removal (iron-nitrogen (Fe-N)-biochar), 96 % amoxicillin degradation (Stenotrophomonas sp. WA5) and 70–95 % quinolone removal (hybrid wetlands). Long-term field data, harmonised risk frameworks and fate data for metabolites, weathered MPs and metal complexes remain limited, warranting priority research attention.