Challenges in the Measurement of Antibiotics and in Evaluating Their Impacts in Agroecosystems: A Critical Review

Abstract

Large quantities of antibiotics are used in agricultural production, resulting in their release to agroecosystems through numerous pathways, including land application of contaminated manure, runoff from manure-fertilized fields, and wastewater irrigation of croplands. Antibiotics and their transformation products (TPs) exhibit a wide range of physico-chemical and biological properties and thus present substantive analytical challenges. Advances in the measurement of these compounds in various environmental compartments (plants, manure, soil, sediment, and water) have uncovered a previously unrealized landscape of antibiotic residues. These advanced multiresidue methods, designed to measure subng g -1 concentrations in complex mixtures, remain limited by the inherent intricacy of the sample matrices and the difficultly in eliminating interferences that affect antibiotic detection. While efficient extraction methods combined with high sensitivity analysis by liquid chromatography/mass spectrometry can provide accurate quantification of antibiotics and their TPs, measured concentrations do not necessarily reflect their bioavailable fractions and effects in the environment. Consequently, there is a need to complement chemical analysis with biological assays that can provide information on bioavailability, biological activity, and effects of mixtures. Enzyme-linked immunosorbent assays (ELISA), often used as screening tools for antibiotic residues, may be useful for detecting the presence of structurally related antibiotic mixtures but not their effects. Other tools, including bioreporter assays, hold promise in measuring bioavailable antibiotics and could provide insights on their biological activity. Improved assessment of the ecological and human health risks associated with antibiotics in agroecosystems requires continued advances in analytical accuracy and sensitivity through improvements in sample preparation, instrumentation, and screening technologies.

Review of Antimicrobial Resistance in the Environment and Its Relevance to Environmental Regulators

“…Toxicological and AMR selection risks cannot be easily predicted from solely knowing the concentration of antibiotics, metals and biocides owing to significant uncertainties in bioavailability (Jechalke et al, 2014; Aga et al, 2016). Fluoroquinolones have been shown to be relatively biounavailable in some sludge amended soils, which was not correlated with any significant change to the ecosystem services: nitrification and denitrification; however, community structure and other ecosystem services might have been impacted, but were not examined (Rosendahl et al, 2012).…”

Irrigation Water Quality—A Contemporary Perspective

“…Environmental contamination by antibiotic residues in food production systems is a growing problem worldwide, and the potential implications to proliferation of antibiotic resistance have been the subject of multiple reviews and opinion articles [58][59][60]. The occurrence of persistent antibiotic residues in various water sources [61,62] is well documented which not only includes municipal [63,64], agricultural [65,66] and hospital sewage [67,68] but also groundwater [69] and surface water [70][71][72]. The concentration range of antibiotics is generally measured at ng L −1 to a few µg L −1 in many water sources [73], though concentrated wastewater can have much higher levels [65].…”

“…The occurrence of persistent antibiotic residues in various water sources [61,62] is well documented which not only includes municipal [63,64], agricultural [65,66] and hospital sewage [67,68] but also groundwater [69] and surface water [70][71][72]. The concentration range of antibiotics is generally measured at ng L −1 to a few µg L −1 in many water sources [73], though concentrated wastewater can have much higher levels [65]. Recent studies have demonstrated that plants can take up antibiotics (like amoxicillin, ketoconazole, lincomycin, oxytetracycline, sulfamethoxazole, sulfonamides, and tetracyclines) [74][75][76] and antibiotic contaminated irrigation water can play a significant role in the uptake [77].…”

Antibiotics in Agroecosystems: Introduction to the Special Section

“…Not only is the wide variety of antibiotic compounds of concern, but some of their transformation products and metabolites may also affect biological activity and therefore need to be considered when conducting environmental studies. Aga et al (2016) examine the state of the science for detection, quantification, and risk assessment of antibiotics and their transformation products in the agroecosystem.…”