| Abstract |
The extensive use of antibiotics in livestock farming can be uncontrollable. The misuse
of them (controlled or not), results in the appearance of antibiotic residues into dairy
products, which poses as a threat to the human’s health. The more the usage of
antibiotics increases, the greater are the chances of residues to be found. . The aim of the
current research was the determination of the levels of sulfonamides (SA’s),
tetracyclines (TC’s), streptomycin (STR), and fluoroquinolones (FQNL’s) in milk
samples during autumn and winter season.
The Enzyme-linked Immunosorbent Assay (ELISA) was the technique used for this
research. The detection limits of this method were 5 μg/L for the STR, 0.9 μg/L for the
TC’s, 3.5 μg/L for the SA’s and 3 μg/L for the FQNL’s.
The samples of commercial and raw milk were collected from the local markets and
dairies in Heraklion, and their total number was 42 in each season. In order for the
samples to be analyzed, they were separated according to the animal derivation into
cow, goat and cattle milk. Further grading was based on the milk’s fat.
During the autumn season, 35.7% was found positive in TC’s and 26.2% in FQNL’s.
STR’s and SA’s percentages were found significantly lower, with 4.8% and 11.9%,
respectively. The average detected concentrations of SA’s, STR and TC’s were detected
5.62 (range: 4.22-5.93 μg/L), 8.91 (range: 5.33-12.49 μg/L) and 1.87 (range: 0.95-5.84
μg/L) μg/L, respectively. In addition, the average concentration of FQNL’s was 19.60
μg/L (range: 3.08-118.13 μg/L), which was much higher than the others.
During winter, all samples (100%) were positive in TC’s (average: 2.40 μg/L range:
0.97-3.59 μg/L), while 19% of them were positive in STR (average: 7.69 μg/L range:
5.69-12.61 μg/L). On the other hand, none of the samples were positive in FQNL’s and
SA’s, in this period.
Between different types of milk (cow, goat, cattle) various positivity levels and
concentrations were detected. In autumn samples, the biggest amount of antibiotic
residues was found in cow milk. In specific, 17.9% of cow samples were positive in
SA’s (average: 5,62 μg/L), 50% in TC’s (average: 1,59 μg/L) and 32,1% in FQNL’s
(average: 22,24 μg/L), while STR was not detected in any sample. In goat milk, STR
and TC’s were found in 10% and FQNL’s in 20% with average concentrations 12,49,
5,84 and 7,71 μg/L μg/L respectively. None of the goat samples were found to be
positive in SA’s. Lastly, the only antibiotic residue that was detected in cattle milk was
STR (25%) with average 5,33 μg/L.
Different results appeared in the winter period’s research. More specifically, all of the
samples were positive only in TC’s and STR. Average concentrations in cow milk was
2,74 μg/L (100%) for TC’s and 8,47 μg/L (10,7%) for STR, in goat milk 1,73 μg/L
(100%) and 6,97 μg/L (10%) and in cattle milk 1,68 μg/L (100%) and 7,29 μg/L (100%)
μg/L.
It is important to highlight that a cow sample (118,13 μg/L) exceeded acceptable
European Residue Limits for fluoroquinolones (Maximum Residue Levels, MRL’sCommission Regulation (EU) no 37/2010).
In order to measure the exposure of human health to the antibiotic residues (received
from the food chain) a risk assessment took place by calculating the estimated daily
intake (EDI) and the hazard index (HI). For this reason the acceptable daily intake
(ADI) of each antibiotic was used. More specific, the ADI, according to E.U., for SA’s
and STR was 5 μg/kg bw, for TC’s was 3 μg/kg bw and for FQNL’s was 15 μg/kg bw.
The results of this research showed that the EDI and HI were much lower than those of
ADI for all the antibiotics, with HI being lower than 1,5%. Taking into account all the
different ages that consume milk (1, 3, 5, 7, 12, 20, 30 years old), EDI was higher for the
FQNL’s, while HI was higher for the TC’s, though no significant differences were
found.
Researches on the detection of SA’s, TC’s, FQNL’s and STR residues in milk samples,
with ELISA method, are quite limited in E.U. countries, such as ours. This research is
highly innovative regarding this topic, while further studies are required in order to
assess the danger for human health due to nutrition.
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