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The effect of ultralow-dose antibiotics exposure on soil nitrate and N2O flux.

DeVries SL, Loving M, Li X, Zhang P - Sci Rep (2015)

Bottom Line: Under anaerobic incubation conditions, three antibiotics produced statistically significant dose response curves in which denitrification was stimulated at some doses and inhibited at others.Narasin also showed evidence of stimulating denitrification in anaerobic soils within 3 days of exposure, which is concurrent to a statistically significant increase in N2O flux measured over moist soils exposed to similar doses.The observation that even ultralow levels of residual antibiotics may significantly alter the biogeochemical cycle of nitrogen in soil raises a number of concerns pertaining to agriculture, management of nitrogen pollution, and climate change, and warrants additional investigations.

View Article: PubMed Central - PubMed

Affiliation: Department of Earth and Atmospheric Sciences, City College of New York, 160 Convent Avenue, New York, NY, 10031, USA.

ABSTRACT
Exposure to sub-inhibitory concentrations of antibiotics has been shown to alter the metabolic activity of micro-organisms, but the impact on soil denitrification and N2O production has rarely been reported. In this study, incubation and column transport experiments were conducted on soils exposed to as many as four antibiotics in the ng · kg(-1) range (several orders of magnitude below typical exposure rates) to evaluate the impact of ultralow dose exposure on net nitrate losses and soil N2O flux over time. Under anaerobic incubation conditions, three antibiotics produced statistically significant dose response curves in which denitrification was stimulated at some doses and inhibited at others. Sulfamethoxazole in particular had a stimulatory effect at ultralow doses, an effect also evidenced by a near 17% increase in nitrate removal during column transport. Narasin also showed evidence of stimulating denitrification in anaerobic soils within 3 days of exposure, which is concurrent to a statistically significant increase in N2O flux measured over moist soils exposed to similar doses. The observation that even ultralow levels of residual antibiotics may significantly alter the biogeochemical cycle of nitrogen in soil raises a number of concerns pertaining to agriculture, management of nitrogen pollution, and climate change, and warrants additional investigations.

No MeSH data available.


Related in: MedlinePlus

Percent influent nitrate removed from control (o) and experimental (☐) columns during transport through saturated soil columns receiving a continuous flow of nitrate nitrogen and glucose.Experimental columns were spiked with 1 ng·L−1 SMX from t = 24 to t = 108. Triplicate columns were run for the spiked as well as the control tests. Statistically different nitrate reduction (p < 0.05) was observed from t = 30 to t = 108 and is indicated with solid markers.
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f2: Percent influent nitrate removed from control (o) and experimental (☐) columns during transport through saturated soil columns receiving a continuous flow of nitrate nitrogen and glucose.Experimental columns were spiked with 1 ng·L−1 SMX from t = 24 to t = 108. Triplicate columns were run for the spiked as well as the control tests. Statistically different nitrate reduction (p < 0.05) was observed from t = 30 to t = 108 and is indicated with solid markers.

Mentions: Where the effects of antibiotics on soil function have been evaluated, denitrification has consistently been shown to be inhibited where higher doses of antibiotics (>500 μg·kg−1) were administered to soil2, sediment52526 and groundwater327. The consistency of these results contrast greatly to the combined stimulation and inhibition reported here for ng·kg−1 doses in anaerobic soils and further to the results of anaerobic column experiments. Figure 2 illustrates effluent nitrate concentration (as a % of influent concentration) for a set of six columns receiving a 1 mM nitrate influent solution. Starting from t = 24 hours, 1 ng·L−1 SMX was continuously added to the influent of three of these columns. Prior to the addition of SMX, approximately 60% of influent nitrate was reduced during transit through each of the six columns. As the experiment continued, nitrate reduction in the three control columns showed slight diurnal variations, possibly resulting from temperature changes in the laboratory, but the overall average remained relatively constant at ~60%. In contrast, the columns receiving influent spiked with 1 ng·L−1 SMX showed an increase in overall nitrate reduction, with total nitrate losses increasing from an initial 60% to nearly 90% at the end of the experiment. According to student t-tests, this increase is statistically significant at or above the 95% confidence level from t = 30 through the end of the experiment (see Supplementary Information). Unlike the anaerobic incubation experiment where the maximum stimulatory effect of SMX was observed on Day 1, stimulation in the column experiments appears to steadily increase over time. The discrepancy between these results may indicate that the stimulatory effect of SMX at the 1 ng·kg−1 or 1 ng·L−1 level is reduced over time by biodegradation. The soil used for the anaerobic incubation experiment received only a single dose of SMX at the beginning of the experiment whereas the columns received a steady supply of SMX-spiked influent that was prepared daily. The gradual increase in denitrification rate relative to the control might indicate that any microbial shift resulting from 1 ng·L−1 SMX exposure is both maintained and enhanced by continued antibiotic pressure at this dose.


The effect of ultralow-dose antibiotics exposure on soil nitrate and N2O flux.

DeVries SL, Loving M, Li X, Zhang P - Sci Rep (2015)

Percent influent nitrate removed from control (o) and experimental (☐) columns during transport through saturated soil columns receiving a continuous flow of nitrate nitrogen and glucose.Experimental columns were spiked with 1 ng·L−1 SMX from t = 24 to t = 108. Triplicate columns were run for the spiked as well as the control tests. Statistically different nitrate reduction (p < 0.05) was observed from t = 30 to t = 108 and is indicated with solid markers.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4660347&req=5

f2: Percent influent nitrate removed from control (o) and experimental (☐) columns during transport through saturated soil columns receiving a continuous flow of nitrate nitrogen and glucose.Experimental columns were spiked with 1 ng·L−1 SMX from t = 24 to t = 108. Triplicate columns were run for the spiked as well as the control tests. Statistically different nitrate reduction (p < 0.05) was observed from t = 30 to t = 108 and is indicated with solid markers.
Mentions: Where the effects of antibiotics on soil function have been evaluated, denitrification has consistently been shown to be inhibited where higher doses of antibiotics (>500 μg·kg−1) were administered to soil2, sediment52526 and groundwater327. The consistency of these results contrast greatly to the combined stimulation and inhibition reported here for ng·kg−1 doses in anaerobic soils and further to the results of anaerobic column experiments. Figure 2 illustrates effluent nitrate concentration (as a % of influent concentration) for a set of six columns receiving a 1 mM nitrate influent solution. Starting from t = 24 hours, 1 ng·L−1 SMX was continuously added to the influent of three of these columns. Prior to the addition of SMX, approximately 60% of influent nitrate was reduced during transit through each of the six columns. As the experiment continued, nitrate reduction in the three control columns showed slight diurnal variations, possibly resulting from temperature changes in the laboratory, but the overall average remained relatively constant at ~60%. In contrast, the columns receiving influent spiked with 1 ng·L−1 SMX showed an increase in overall nitrate reduction, with total nitrate losses increasing from an initial 60% to nearly 90% at the end of the experiment. According to student t-tests, this increase is statistically significant at or above the 95% confidence level from t = 30 through the end of the experiment (see Supplementary Information). Unlike the anaerobic incubation experiment where the maximum stimulatory effect of SMX was observed on Day 1, stimulation in the column experiments appears to steadily increase over time. The discrepancy between these results may indicate that the stimulatory effect of SMX at the 1 ng·kg−1 or 1 ng·L−1 level is reduced over time by biodegradation. The soil used for the anaerobic incubation experiment received only a single dose of SMX at the beginning of the experiment whereas the columns received a steady supply of SMX-spiked influent that was prepared daily. The gradual increase in denitrification rate relative to the control might indicate that any microbial shift resulting from 1 ng·L−1 SMX exposure is both maintained and enhanced by continued antibiotic pressure at this dose.

Bottom Line: Under anaerobic incubation conditions, three antibiotics produced statistically significant dose response curves in which denitrification was stimulated at some doses and inhibited at others.Narasin also showed evidence of stimulating denitrification in anaerobic soils within 3 days of exposure, which is concurrent to a statistically significant increase in N2O flux measured over moist soils exposed to similar doses.The observation that even ultralow levels of residual antibiotics may significantly alter the biogeochemical cycle of nitrogen in soil raises a number of concerns pertaining to agriculture, management of nitrogen pollution, and climate change, and warrants additional investigations.

View Article: PubMed Central - PubMed

Affiliation: Department of Earth and Atmospheric Sciences, City College of New York, 160 Convent Avenue, New York, NY, 10031, USA.

ABSTRACT
Exposure to sub-inhibitory concentrations of antibiotics has been shown to alter the metabolic activity of micro-organisms, but the impact on soil denitrification and N2O production has rarely been reported. In this study, incubation and column transport experiments were conducted on soils exposed to as many as four antibiotics in the ng · kg(-1) range (several orders of magnitude below typical exposure rates) to evaluate the impact of ultralow dose exposure on net nitrate losses and soil N2O flux over time. Under anaerobic incubation conditions, three antibiotics produced statistically significant dose response curves in which denitrification was stimulated at some doses and inhibited at others. Sulfamethoxazole in particular had a stimulatory effect at ultralow doses, an effect also evidenced by a near 17% increase in nitrate removal during column transport. Narasin also showed evidence of stimulating denitrification in anaerobic soils within 3 days of exposure, which is concurrent to a statistically significant increase in N2O flux measured over moist soils exposed to similar doses. The observation that even ultralow levels of residual antibiotics may significantly alter the biogeochemical cycle of nitrogen in soil raises a number of concerns pertaining to agriculture, management of nitrogen pollution, and climate change, and warrants additional investigations.

No MeSH data available.


Related in: MedlinePlus