Effects of Antibiotics on Plant Growth and Soil Microbial and Enzymatic Activities - Research Paper Example

Different antibiotics have different effects on a plant, while different plants react differently to a certain antibiotic. What this study was trying to find out are the specific effects of sulfonamides, tetracyclines, tylosin, and trimethoprim on the soil and the plants that depend on it, especially when available data regarding it are scarce and inconsistent. This is important for farmers of agricultural crops such as rice who are using or considering the use of animal manure or treated urine for fertilizer and hydration, respectively.    

Briefly, different concentrations of analytical grade tetracyclines (chlortetracycline and tetracycline), tylosin, sulfonamides (sulfamethazole and sulfamethazine), and trimethoprim were tested for their phytotoxicity of sweet oat, rice, and cucumber through observing their seed germination and plant growth. Tylosin and trimethoprim were included because they are used together with tetracyclines and sulfonamides, respectively. The seeds of sweet oat were the most susceptible to antibiotics, and sulfonamides and tetracyclines had greater effects on seed germination, as compared to tylosin and trimethoprim. In contrast, growth inhibition, especially of rice, was achieved only with sulfonamides. This is because sorption coefficients of sulfonamides are very low in the soil as compared to that of tetracyclines, making the former more bioavailable and the latter less likely to be absorbed by the plant.

As well, their impact on soil microbial activity was assessed through the observation of their effects on soil respiration and soil phosphatase activity. Soil respiration was greatly affected upon exposure to sulfamethazole, sulfamethazine, and trimethoprim, with the first being the most potent and the last being the least, although the recovery of respiration 4 days after the application was observed. This is because the dissipation half-life of sulfonamides is 2 to 5, making the antibiotic concentration after 4 days greatly depleted. On the other hand, all six antibiotics were found to inhibit phosphatase activity        

            Despite the seemingly breakthrough results of the study, it is of little use, because the concentrations used do not reflect the amount of antibiotics crops are actually exposed to in agriculture. For example, seed germination was affected by sulfonamides at 300 mg/L, when in fact animal manure contains at most 91 mg/kg of the antibiotic. This means that a plant should be given more than 3 kg of manure for the adverse effects of sulfonamide can be considered. However, this is almost impossible in a real setting. The researchers could have instead used other antibiotics that have a higher concentration in manure rather than sulfonamides and tetracyclines, probably penicillin and streptomycin, because of their greater propensity of use.

In relation, other plants should have been considered in this study. Although rice is an important commodity, so are corn, wheat, and potatoes, which have been conspicuously left out. Probably, the data on rice was thought to be applicable to its closest relatives, corn and wheat. However, testing potatoes is important, because, in my opinion, underground plants such as potatoes are affected the most by the so-called antibiotic pollutants.