Effects of pine bark amendment on the transport of sulfonamide antibiotics in soils

In the present work, laboratory column experiments were carried out to study the effect of pine bark amendment (at doses of 0, 12, 48 and 96 Mg ha^-1) on the transport of three sulfonamide antibiotics (sulfadiazine -SDZ-, sulfamethazine -SMT-, and sulfachloropyridazine -SCP-) through two crop soils. All three sulfonamides showed high mobility in the unamend soils, with absence of retention in most cases. However, some differences were detected regarding the degree of interactions between sulfonamides and soils, being higher for soil 1, which was attributed to its higher organic carbon content. For both soils, interactions with the antibiotics studied followed the sequence SDZ < SMT < SCP, indicating an increase as a function of the hydrophobicity of sulfonamides. Pine bark amendment significantly increased the retention of the three sulfonamides in both soils. Specifically, in the case of soil 1, the incorporation of the highest dose of pine bark (96 Mg ha^-1) caused that retention increased from 0% to 70.3% for SDZ, from 2.7% to 71.3% for SMT, and from 0% to 85.4% for SCP. This effect of pine bark is mainly attributed to its high organic carbon content (48.6%), including substances with potential to interact and retain antibiotics, as well as to its acidic pH (4.5). Therefore, pine bark amendment would be an effective alternative to reduce the transport of sulfonamides in soils and, thus, decrease risks of passing to other environmental compartments, as well as harmful effects on the environment and public health.