The presence of antibiotics in crops is mainly caused by their irrigation with reclaimed wastewater and by the use of organic amendments of animal origin. During this work, the fate of sulfonamide antibiotics in tomato crop has been assessed in two commercial greenhouses located in Almería (Spain) irrigated with reclaimed wastewater. Samplings were made annually for two years. Sulfonamides in several parts of the plant (roots, leaves and fruits) as well as reclaimed wastewater, amendments and soils were analyzed by UHPLC-MS/MS. The results showed that sulfonamides accumulated in soils (sulfamethoxazole between 2 and 14 µg Kg−1; sulfadiazine, sulfathiazole, sulfapyridine, sulfamerazine and sulfadimethoxine in concentrations below 1 µg Kg−1) were in the reclaimed wastewater at concentrations in the ng L−1 range. Their distribution in plants depended on the sulfonamide. The sulfonamides detected in tomato were sulfadiazine, sulfapyridine, sulfamethazole, sulfamethoxazole and sulfadimethoxine. Sulfamethoxazole was the antibiotic with highest concentration in tomato fruit, exceeding 30 µg Kg−1. All sulfonamides were below the Acceptable Daily Intake, however, further studies and legislation are needed to assure food safety.
A double strategy based on the removal of sulfonamide antibiotics by Pleurotus ostreatus and adsorption on spent mushroom substrate was assessed to reclaim contaminated wastewater. P. ostreatus was firstly tested a in liquid medium fortified with five sulfonamides: sulfamethoxazole, sulfadiazine, sulfathiazole, sulfapyridine and sulfamethazine, to evaluate its capacity to remove them, to test for any adverse effects on fungal growth and for any reduction in residual antibiotic activity. P. ostreatus was effective in removing sulfonamides up to 83 to 91 % of the applied doses over 14 days. The antibiotic activity of the sulfonamide residues was reduced by 50 %. Sulfamethoxazole transformation products by laccase were identified and the degradation pathway was proposed. In addition, P. ostreatus growth on a semi-solid medium of spent mushroom substrate and malt extract agar was used to develop a biofilter for the removal of sulfonamides from real wastewater. The biofilter was able to remove more than 90% of the sulfonamide concentrations over 24 hours by combining adsorption and biodegradation mechanisms.
The application of organic amendments to contaminated agricultural lands can immobilize metals and improve soil conditions. The chemical structures and long-term stability of commercial humic substances and other composted organic amendments (sheep and horse manure, vermicompost, pine bark, and pruning waste) were analyzed using 13C CPMAS NMR, FT-IR, and DSC to evaluate their use in soil remediation. The interactions of humic substances and manure with Cu (0 and 5000 mg kg−1) at different pH (2.5 and 5.0) were studied through a batch adsorption experiment observing the changes in their molecular structure using spectroscopic techniques. Humic substances exhibited high aromaticity and phenolic and carboxylic group content, with great affinity for Cu complexation. Humic substances and pruning waste were the most stable due to their high recalcitrant organic matter contents, whereas manure was the least stable, given the labile nature of its organic matter content. There were considerable changes in the carboxylic and phenolic groups of humic substances with pH, and also with Cu, albeit in a lesser extent, especially at pH 5.0, suggesting the great sorption capacity of humic substances and the key role of pH and these functional groups in metal complexation. Manure did not exhibit such changes. Commercial humic substances could be useful amendments for the remediation of contaminated agricultural soils due to their high sorption capacities and long-term stability.
The aim of this study was to determine the effects of new Micro Carbon Technology (MCT®) fertilizers based on humic acids biologically digested on the growth and development of pepper plants. In this work, the biostimulant effect of MCT® fertilizers was compared to conventional mineral fertilizers. In order to evaluate MCT® fertilizers, a previous chemical characterization (infrared spectroscopy, liquid chromatography and mass spectrometry) of seven MCT® fertilizers was performed. Two fertilization tests of pepper plants were carried out in hydroponic conditions, where the fertilization and the age of the plants were studied in order to evaluate the specific effects on roots and leaves. Plant weight and foliar analysis (chlorophyll indices and nutrients) have been determined. Transmission electron microscopy was used to visualize the morphological differences in the root and leaf cells. Comparison between conventional and MCT® based fertilizers showed that, with the MCT® fertilizers, the plant is exposed to the presence of free amino acids (Glycine and Alanine), polyphenols and humic substances. Although no significant differences were found in plant mass production, the plants fertilized with MCT® products presented better nutritional status than plants treated with conventional fertilization in terms of nutrient content in leaves. Important morphological differences in root cells were found. A large central vacuole that represented the 68–83% of the total root cell area was shown if the MCT® products were used, suggesting significant changes of membrane permeability in terms of water adsorption and consequently nutrient storage. The morphological differences observed in the root cells were more noticeable in adult plants.
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