Antibiotics in livestock
Antibiotics are essential to raising livestock and are usually given to farm animals by mixing them with food. Antibiotics that aren’t absorbed by the animal during digestion are excreted in excrement and end up in the soil.
Are plants affected by antibiotics ?
The antibiotics in manured soil can be taken up by plants and accumulate in different parts of the plant. Bioaccumulation of toxic materials in plants can result in reduced and abnormal growth of the roots, shoots, leaves, root decay, reduced rate of germination as well as metabolic activities and so on. However, some chemicals may have positive effects on the plants as well. The effects of the antibiotics on plants vary with the types and modes of action of the drugs, the dosage, and the plant species.
So far, studies investigating antibiotic uptake in plants have mostly focused on crop plants, but non-crop plants might be adversely affected as well. Plus, most of these studies are done in the lab, so they could miss out on the actual events that take place in field. Also, many experiments have used unrealistically high concentrations of antibiotics. Therefore, a recent study by Minden et al. used antibiotics in concentrations similar to those measured in the field and included non-crop plants.
Is the effect of antibiotics similar in non-crop plants?
The researchers used two commonly grown crops, wheat (Triticum aestivum) and summer rapeseed (Brassica napus) and two non-crop plants which are the grass species- called the sheperd’s purse (Capsella bursa-pastoris) and loose silky-bent (Apera spica-venti). Three commonly used antibiotics of livestock- penicillin G sodium salt, sulfadiazine, and tetracycline were applied to both crop plants and non-crop plants. These three antibiotics are most commonly used in livestock in Europe and have completely different mechanisms of action. Plus, they remain stable in the soil for a long time. The researchers applied three different concentrations of each of the antibiotics to their seeds before and after germination and measured the growth rates of the plants. Simultaneously, plants without any antibiotics were used as controls to tease out the effects of antibiotics uptake.
The researchers witnessed a delay in germination for three out of the four plants that were exposed to higher concentrations of antibiotics. The grass sheperd’s purse (Capsella bursa-pastoris) did not germinate at all regardless of the antibiotics concentrations, probably, due to the poor quality of seeds. Additionally, the response of the four plants to the antibiotics were not absolutely positive or negative, rather it was species as well as size specific.
Source: photograph by Balaram Mahalder, distributed under a CC BY-SA 3.0 license.
The antibiotics used in livestock farming are usually present in soils at low concentrations, nevertheless this can significantly affect the germination time of crops. This study also showed that non-crop plants, which are usually grown along the margins of these farmlands, can be affected by antibiotics in soil. Whether any effect will be induced depends on the type of non-crop plants growing along the fields. In the future, more research is needed on effects of low concentrations of antibiotics on these non-crop species, and on the influence of the soil microbes on uptake of antibiotics.
Literature: Minden, V., Deloy, A., Volkert, A. M., Leonhardt, S. D., & Pufal, G. (2017). Antibiotics impact plant traits, even at small concentrations. AoB Plants, 9(2). doi: 10.1093/aobpla/plx010