Journal Article

Accumulation of Pharmaceuticals, Enterococcus, and Resistance Genes in Soils Irrigated with Wastewater for Zero to 100 Years in Central Mexico

Broszat, Melanie, Willaschek, Elisha, Siemens, Jan, Dalkmann, Philipp, Grohmann, Elisabeth, Sakinc, Tuerkan, Siebe, Christina, Amelung, Wulf, Huebner, Johannes

2012

Overview

Irrigation with wastewater releases pharmaceuticals, pathogenic bacteria, and resistance genes, but little is known about the accumulation of these contaminants in the environment when wastewater is applied for decades. We sampled a chronosequence of soils that were variously irrigated with wastewater from zero up to 100 years in the Mezquital Valley, Mexico, and investigated the accumulation of ciprofloxacin, enrofloxacin, sulfamethoxazole, trimethoprim, clarithromycin, carbamazepine, bezafibrate, naproxen, diclofenac, as well as the occurrence of Enterococcus spp., and sul and qnr resistance genes. Total concentrations of ciprofloxacin, sulfamethoxazole, and carbamazepine increased with irrigation duration reaching 95% of their upper limit of 1.4 µg/kg (ciprofloxacin), 4.3 µg/kg (sulfamethoxazole), and 5.4 µg/kg (carbamazepine) in soils irrigated for 19-28 years. Accumulation was soil-type-specific, with largest accumulation rates in Leptosols and no time-trend in Vertisols. Acidic pharmaceuticals (diclofenac, naproxen, bezafibrate) were not retained and thus did not accumulate in soils. We did not detect qnrA genes, but qnrS and qnrB genes were found in two of the irrigated soils. Relative concentrations of sul1 genes in irrigated soils were two orders of magnitude larger (3.15 × 10(-3) ± 0.22 × 10(-3) copies/16S rDNA) than in non-irrigated soils (4.35 × 10(-5)± 1.00 × 10(-5) copies/16S rDNA), while those of sul2 exceeded the ones in non-irrigated soils still by a factor of 22 (6.61 × 10(-4) ± 0.59 × 10(-4) versus 2.99 × 10(-5) ± 0.26 × 10(-5) copies/16S rDNA). Absolute numbers of sul genes continued to increase with prolonging irrigation together with Enterococcus spp. 23S rDNA and total 16S rDNA contents. Increasing total concentrations of antibiotics in soil are not accompanied by increasing relative abundances of resistance genes. Nevertheless, wastewater irrigation enlarges the absolute concentration of resistance genes in soils due to a long-term increase in total microbial biomass.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Accumulation / Agricultural Irrigation / Agriculture / Anti-Bacterial Agents - analysis / Antibiotics / Bacteria / Bezafibrate / Biological Products - analysis / Biology / Carbamazepine / Causes of / Chemical wastes / Chemistry / Chromatography / Ciprofloxacin / Clarithromycin / Climate change / Contaminants / Crop diseases / Crop science / Diclofenac / Drug resistance / Drug Resistance, Multiple, Bacterial - genetics / Drugs / Earth Sciences / Ecology / Engineering / Enrofloxacin / Enterococcus / Enterococcus - genetics / Enterococcus - isolation & purification / Environmental aspects / Environmental Monitoring / Escherichia coli Proteins - genetics / Escherichia coli Proteins - isolation & purification / Genes / Genetic aspects / Infectious diseases / Influence / Irrigation / Medicine / Mexico / Microbial drug resistance / Microorganisms / Naproxen / Neural networks / Personal grooming / Pharmaceuticals / Prescription Drugs - analysis / Public health / RNA, Ribosomal, 16S - genetics / rRNA 16S / Sludge / Soil - chemistry / Soil contamination / Soil Microbiology / Soil Pollutants - analysis / Soil sciences / Soils / Sulfamethoxazole / Time Factors / Trimethoprim / Valleys / Vertisols / Waste Water - chemistry / Waste Water - microbiology / Wastewater / Wastewater irrigation / Wastewater pollution / Water shortages / Water treatment