| Biosolids, or composted sewage sludge, are a relatively untapped but broadly available resource, and the repository for a substantial portion of nutrients consumed in the form of food. Returning these nutrients to food production systems would "close the loop" in nutrient cycling rather than cause a waste disposal problem. Biosolids have the potential to be a beneficial soil amendment to agricultural land, yet in addition to nutrients they also ubiquitously contain contaminants such as pharmaceuticals and personal care products (PPCPs). Biochar, or pyrolyzed agricultural waste, is a potential co-amendment with biosolids that could reduce the bioavailability of pharmaceuticals found in biosolids. Because of its unique chemistry and high surface area, biochar can sorb organic chemicals such as PPCPs that are introduced to the soil via application of biosolids. The major objectives of this work were to understand effects of contaminants found in biosolids on soil ecosystem processes and related microbial structure, and to examine how biochar affects these relationships. These were addressed in two separate studies: (1) In a laboratory soil incubation, we show that functional redundancy between ammonia-oxidizing bacteria (AOB) and archaea (AOA) can buffer negative effects of exposure to ciprofloxacin, an antibiotic commonly found in biosolids. The higher resistance, at least in the short-term, of AOA to antibiotics can maintain the process rate of nitrification, providing ecosystem functional resistance to the antibiotic disturbance. Further, co-amending with biochar mitigates any negative effect of ciprofloxacin on either AOB or AOA, suggesting that biochar can be an effective sorbent of pharmaceutical contaminants. (2) In a greenhouse study examining the effects of co-amending biosolids with biochar, we find that biochar has positive growth effects on plants, possibly due to the aforementioned sorption of growth-limiting contaminants found in biosolids. However, a bioanalytical (CALUX) examination of endocrine-disrupting activity in the biosolid- and biochar-amended soils suggests that biochars might also be a source of such activity. The rate of biochar application to induce this effect (100 t ha -1) is high above the average agronomic rate (10 t ha-1), and it is thus possible that such levels of endocrine-disrupting activity would not be present in the soil in an agricultural context. Together, these results show how microbial communities and related functions are affected by contaminants in biosolids, and suggest that biochar might be an effective co-amendment to mitigate negative effects of an antibiotic disturbance. However, biochar must be explored for potential environmentally-relevant endocrine-disrupting activity before it is used as a remediation tool. |
