Antibiotika in Wirtschaftsdüngern, Klärschlämmen und Gärresten und deren Interaktion mit Pflanzen

Manure, digestates and sewage sludge are produced in large amounts and are used in agriculture because of their nutrient concentration. Through application they can carry pollutants like heavy metals and antibiotics into agricultural soils.

The aim of this work was to evaluate the methodological basics of analysis for the phosphorus (P) content in manure, digestates and sewage sludge and the development of a suitable analytical method especially for antibiotics in these
complex matrices. Acute and combinatory toxic effects of heavy metals and antibiotics were investigated in a pot trial and in model experiments to estimate their ecological relevance.

This work provided the following results:

The extraction of P by CAL delivered more reasonable results than a water extraction because CAL extraction was less affected by the matrix. CAL and NAC extraction delivered comparable results so both can be used to determine the P content in digestates. It was shown that the P determination by ICP-OES was more suitable to determine the P content in comparison to the colorimetric measurement by a spectral photometer as P contents were partly overestimated.

The median and maximum concentrations of antibiotics tend to be lower in digestates than in the substrates of the anaerobic fermentation. However, the contaminations were in the same order of magnitude. Median antibiotic concentrations in manure, digestate and sewage sludge samples were in the range of 100 μg to a few mg kg-1 on a dry matter basis. The maximum concentration determined in a digestate was 29.8 mg tetracycline kg-1 DW.

In small-scale tests (toxkits) it was proven that antibiotics in high concentrations are toxic to Daphnia magna and Sinapis alba. Daphnia magna was immobilised by high antibiotic concentrations and in case of Sinapis alba the root length was reduced by high concentrations of antibiotics. In the toxkits experiments the antibiotics enrofloxacine, sulfadiazine and tetracycline revealed synergistic toxic effects incombination. In a pot experiment, where the combinatory effect of enrofloxacin and copper on growth of Sinapis alba was investigated, it was shown that no enrofloxacin could be detected in the soil solution. This indicates a high adsorption of enrofloxacin to the soil-matrix. In concentrations of 3.6 mg kg-1 soil enrofloxacin caused a reduction in biomass development of Sinapis alba and could be detected in the plant material.

In a worst-case scenario it was calculated that up to 22 μg tetracycline kg-1 soil could be transferred to the field as a result of fertilization. This concentration is significantly lower than the toxic effect concentration which was determined for Sinapis alba. Based on the data obtained in the present work, it can be concluded, that currently no acute toxic effects on plant growth should be expected due to fertilization with manure, digestates and sewage sludge. Nevertheless, other toxic effects which were not evaluated in this work, could pose a risk for the environment.