Soil-dwelling earthworms have also been used to test API toxicity and, like with
epigeic earthworms, the results point out to a certain degree of tolerance. For
example, toxic effects from the antibiotics tylosin and oxytetracycline were assessed
using the endogeic earthworm A. caliginosa incubated in an agricultural sandy loam
soil [107]. The researchers did not find significant effects after 21 days of exposure to
the antibiotic-spiked soils (500–5,000 mg/kg dry soil). Therefore, assuming a certain
degree of tolerance of soil-dwelling earthworm species to APIs, we propose that
inoculation of agricultural soils with earthworms could be an eco-friendly strategy to
alleviate potential toxic effects of these chemicals on soil microbial activity, and to
reduce the uptake of APIs by plants. The next two sections provide an overview on
how earthworms may function as “bioreactors” of API degradation in the feedstocks
to be used as soil amendments as well as in agricultural soils.
5 Pharmaceutical-Contaminated Soil Amendments (Ex Situ
Vermiremediation)
Fertilisation of agricultural soils with biosolids and treated (or untreated) manure is
one of the main routes of soil contamination with APIs. Biosolids are stabilised
organic materials resulting from treatment of municipal or industrial sewage that
meet regulatory guidelines for its application as a soil amendment [108]. It is now
recognised that biosolids application to agricultural lands increase the concentration
of APIs in soil, the risk of surface water and groundwater contamination and the
uptake of API (and metabolites) by plants [109]. Furthermore, biosolids application
is between 5 and 50 times greater in forest and degraded sites than in agricultural
soils [109], which represent a high ecological risk for soil biodiversity and soil
biological processes.
One of the environmental risks of CAFOs is the occurrence of veterinary pharmaceuticals (e.g. antibiotics) in manure [110]. The high consumption of antibiotics
in CAFOs together to the fact that antibiotics are not completely metabolised by
animals [111], lead to their presence in urine and manure. The most frequently
antibiotics found in animal manure belong to fluoroquinolones, sulfonamides and
tetracyclines [110, 111]. Concentrations of these pharmaceuticals may be so high
that direct application of untreated manure to soil is discouraged or forbidden.
Accordingly, manure is aerobically or anaerobically treated to reduce the risk of
soil contamination by APIs and other environmental contaminants and to obtain
thereby value-added organic fertilisers. The most frequent treatments are
composting, anaerobic digestion and accumulation in aerobic/anaerobic open-air
ponds. Among them, composting provides the most technically easy and low-cost
option, but there are still uncertainties about the extent of API biodegradation during
composting. Although composting generally removes >90% of APIs [111], some
studies show that this technique is not efficient for the full elimination of some types
of APIS. For example, 17–31% of the initial concentration of ciprofloxacin
Vermiremediation of Pharmaceutical-Contaminated Soils and Organic Amendments
351
epigeic earthworms, the results point out to a certain degree of tolerance. For
example, toxic effects from the antibiotics tylosin and oxytetracycline were assessed
using the endogeic earthworm A. caliginosa incubated in an agricultural sandy loam
soil [107]. The researchers did not find significant effects after 21 days of exposure to
the antibiotic-spiked soils (500–5,000 mg/kg dry soil). Therefore, assuming a certain
degree of tolerance of soil-dwelling earthworm species to APIs, we propose that
inoculation of agricultural soils with earthworms could be an eco-friendly strategy to
alleviate potential toxic effects of these chemicals on soil microbial activity, and to
reduce the uptake of APIs by plants. The next two sections provide an overview on
how earthworms may function as “bioreactors” of API degradation in the feedstocks
to be used as soil amendments as well as in agricultural soils.
5 Pharmaceutical-Contaminated Soil Amendments (Ex Situ
Vermiremediation)
Fertilisation of agricultural soils with biosolids and treated (or untreated) manure is
one of the main routes of soil contamination with APIs. Biosolids are stabilised
organic materials resulting from treatment of municipal or industrial sewage that
meet regulatory guidelines for its application as a soil amendment [108]. It is now
recognised that biosolids application to agricultural lands increase the concentration
of APIs in soil, the risk of surface water and groundwater contamination and the
uptake of API (and metabolites) by plants [109]. Furthermore, biosolids application
is between 5 and 50 times greater in forest and degraded sites than in agricultural
soils [109], which represent a high ecological risk for soil biodiversity and soil
biological processes.
One of the environmental risks of CAFOs is the occurrence of veterinary pharmaceuticals (e.g. antibiotics) in manure [110]. The high consumption of antibiotics
in CAFOs together to the fact that antibiotics are not completely metabolised by
animals [111], lead to their presence in urine and manure. The most frequently
antibiotics found in animal manure belong to fluoroquinolones, sulfonamides and
tetracyclines [110, 111]. Concentrations of these pharmaceuticals may be so high
that direct application of untreated manure to soil is discouraged or forbidden.
Accordingly, manure is aerobically or anaerobically treated to reduce the risk of
soil contamination by APIs and other environmental contaminants and to obtain
thereby value-added organic fertilisers. The most frequent treatments are
composting, anaerobic digestion and accumulation in aerobic/anaerobic open-air
ponds. Among them, composting provides the most technically easy and low-cost
option, but there are still uncertainties about the extent of API biodegradation during
composting. Although composting generally removes >90% of APIs [111], some
studies show that this technique is not efficient for the full elimination of some types
of APIS. For example, 17–31% of the initial concentration of ciprofloxacin
Vermiremediation of Pharmaceutical-Contaminated Soils and Organic Amendments
351