UCLA

The widespread occurrence of antibiotic resistance and heavy metal are critical public health issues, posing global threats to human health. Antibiotics have been widely used in medical settings and in agriculture as growth promoters in livestock. A large fraction of antibiotics are excreted unchanged and can create selective environments for the emergence and proliferation of antibiotic resistance in receiving environmental compartments such as agricultural soils. Heavy metals, known as notable environmental stressors, promote the proliferation of antibiotic resistance by exerting co-selective pressure. More research is needed to manage both issues and to address the gap in the literature that exists with respect to their synergism. Through both field and laboratory microcosm research, the present study aims to investigate the prevalence, fate, co-occurrence, and interactions of antibiotic resistance genes (ARGs) and metal(loid)s in urban and agricultural soils.

Los Angeles has a long history of lead (Pb) contamination due to automobile emissions, industrial processes, and Pb-containing paint. Although the amount of Pb coming from these sources has been significantly reduced, the legacy of Pb in Los Angeles continues to affect soil Pb concentrations in public parks. These concentrations were shown to be high, with 47 parks having one or more samples exceeding the California EPA guideline of 80 ppm. According to EPA LeadSpread model, soil Pb levels of 80–320 ppm can lead to an estimated increase of blood Pb level from 1 to 4 ug/dL. This study provides information that can be used to guide remediation decisions for authorities and for the construction of Pb-safe environments.

While bioretention systems (biofilters) have been widely and effectively used to capture chemical pollutants from surface runoff, the effect of biofilters on both heavy metals and antibiotic resistance genes (ARGs) has been relatively understudied. A comprehensive survey of seasonal and regional ARGs and metal(loid)s is presented in urban biofilters in this study. Multiple effects of soil properties, bioavailable and total metal(loid)s on ARGs within biofilters were determined using multiple linear regression analysis. This study enhances our knowledge of ARG baseline levels for risk assessment and more strategic development of urban biofilters.

Land application of biosolids is a common practice for recycling and reuse of biosolids. However, the effect of land application of biosolids on soil ARG concentrations still remains elusive. Results indicate that ARGs were higher in biosolids-amended soils than in the surrounding agricultural soils that had not received biosolids. Land-applied biosolids also create selective environments for the emergence and proliferation of ARGs in the environment. Spatial patterns of ARGs in soils also provided insight into the distribution of ARGs and their associations with types of land uses, ultimately leading to better management of soil ARGs.