Ecotoxicological effects of copper oxide nanoparticles (nCuO) on the soil microbial community in a biosolids-amended soil.

This study represents a holistic approach in assessing the effects of copper oxide nanoparticles (nCuO) on microbial health and community structure in soil amended with municipal biosolids. The biosolids were amended with nCuO (<50 nm) and mixed into a sandy loam soil at measured Cu concentrations of 27, 54, 123, 265 and 627 mg Cu kg-1 soil. A suite of tests were used to assess the potential impact of nCuO on microbial growth, activity, and diversity. Microbial growth was determined by the heterotrophic plate count (HPC) method, while microbial diversity was assessed using both community level physiological profiling (CLPP) and 16S ribosomal DNA (rDNA) sequencing. Microbial activity was assessed by examining soil nitrification, organic matter decomposition, soil respiration (basal and substrate induced) and soil enzyme assays for dehydrogenase, phosphatase and ß-glucosidase activities. As a readily soluble positive control, copper sulfate (CuSO4) was used at measured Cu concentrations of 65, 140, 335 and 885 mg Cu kg-1 soil for select tests, and at the highest concentration for the remaining tests. Analysis on Cu bioavailability revealed that extractable Cu2+ was higher in CuSO4-spiked soils than nCuO-spiked soils. At a nCuO exposure concentration of ≤265 mg Cu kg-1 soil, stimulatory effects were observed in nitrification, ß-glucosidase and community level physiological profiling (CLPP) tests. nCuO showed no significant inhibitory effects on the soil microbial growth, activity or diversity at the highest concentration (i.e. 627 mg Cu kg-1 soil), with the exception of the dehydrogenase (i.e. ≥27 mg Cu kg-1 soil) and phosphatase (i.e. 627 mg Cu kg-1 soil) enzyme activities. In contrast, inhibition from CuSO4 at 885 mg Cu kg-1 soil was observed in all tests with the exception of ß-glucosidase enzyme activity. The growth of a Cu tolerant bacterium, Rhodanobacter sp., was observed at 885 mg Cu kg-1 soil (CuSO4).

Effect of silver nano-particles on soil microbial growth, activity and community diversity in a sandy loam soil.

Silver nano-particles (AgNPs) are widely used in a range of consumer products as a result of their antimicrobial properties. Given the broad spectrum of uses, AgNPs have the potential for being released to the environment. As a result, environmental risks associated with AgNPs need to be assessed to aid in the development of regulatory guidelines. Research was performed to assess the effects of AgNPs on soil microbial activity and diversity in a sandy loam soil with an emphasis on using a battery of microbial tests involving multiple endpoints. The test soil was spiked with PVP coated (0.3%) AgNPs at the following concentrations of 49, 124, 287, 723 and 1815 mg Ag kg-1 dry soil. Test controls included an un-amended soil; soil amended with PVP equivalent to the highest PVP concentration of the coated AgNP; and soil amended with humic acid, as 1.8% humic acid was used as a suspension agent for the AgNPs. The impact on soil microbial community was assessed using an array of tests including heterotrophic plate counting, microbial respiration, organic matter decomposition, soil enzyme activity, biological nitrification, community level physiological profiling (CLPP), Ion Torrent™ DNA sequencing and denaturing gradient gel electrophoresis (DGGE). An impact on microbial growth, activity and community diversity was evident from 49 to 1815 mg kg-1 with the median inhibitory concentrations (IC50) as low as 20-31 mg kg-1 depending on the test. AgNP showed a notable impact on microbial functional and genomic diversity. Emergence of a silver tolerant bacterium was observed at AgNP concentrations of 49-287 mg kg-1 after 14-28 days of incubation, but not detectable at 723 and 1815 mg kg-1. The bacterium was identified as Rhodanobacter sp. The study highlighted the effectiveness of using multiple microbial endpoints for inclusion to the environmental risk assessment of nanomaterials.