Effects of cadmium addition on net nitrogen mineralization processes in the urban constructed wetland soils of a Chinese delta

Coexistence of microplastics and Cd alters soil N transformation by affecting enzyme activity and ammonia oxidizer abundance

Interactions between heavy metal and microplastics represent a serious threat to ecosystems and human health, but the effect of their coexistence on the soil N transformation processes is unclear. The mechanism in which metal-polluted soil reacts to additional microplastics stress and their toxicology interactions on soil N transformation were determined by investigating the dynamics of soil microbial N transformation in response to Cd stress and different doses of polythene (PE) microplastics by conducting a 14 days aerobic 15N microcosmic incubation experiment. The gross nitrification rates (n_gross) were decreased by 7.47% and 12.5% in the 1% and 2% (w/w) PE groups, respectively, through the direct effect on enzyme activity (β-glucosidase, N-acetylglucosaminidase, and leucine-aminopeptidase) and the abundance and community composition of ammonia oxidizer. It also exerted indirect effect by reducing nitrification substrate concentrations. PE microplastics (>1% [w/w]) significantly increased the gross N immobilization rate, and this change could have been driven by C/N stoichiometry. Cd stress alone led to a rapid short-term mineralization-immobilization turnover (1.67 times of the control). However, such effect was offset when Cd coexisted with PE microplastics, possibly because Cd was directly adsorbed by PE microplastics, and/or microplastics satisfied the C demand by microorganisms under Cd stress. Our findings demonstrated that the coexistence of microplastics and Cd significantly altered soil N nitrification and immobilization, which would change the N bioavailability in soil and alter the effect N cycling on the ecological environment.

Potential ecological risks of heavy metals and Cd accumulation characteristics of Suaeda salsa under different Cd input and water logging conditions in the Yellow River estuary, China

To improve the remediation of heavy metal pollution by typical wetland vegetation and maintain the health of wetland ecosystems under the water-sediment regulation scheme (WSRS) application, we evaluated the potential ecological risk of heavy metals in surface sediment in the Yellow River estuary affected by the WSRS. The ranges of Cr, Cu, Zn, Cd, and Pb content in surface sediment were 52.44-100.80 mg·kg-1 dry weight (DW), 16.38-21.19 mg·kg-1 DW, 64.77-255.50 mg·kg-1 DW, 0.12-0.24 mg·kg-1 DW, and 5.40-8.63 mg·kg-1 DW, respectively, and potential ecological risk coefficients showed that Cd was associated with moderate potential risk. We further examined effects of Cd in a greenhouse experiment to explore the influence of short-term Cd input and water logging condition changes induced by WSRS on the Cd absorption characteristics of Suaeda salsa (L.) Pall in the Yellow River estuary. The results showed that total biomass decreased but Cd content in tissue of S. salsa increased with increasing Cd input and the accumulation factor reached maximum values at 100 μg·L-1 of Cd, indicating that S. salsa efficiently accumulated Cd. Water logging depth significantly affected S. salsa growth and Cd absorption with deeper water logging being detrimental to growth. The interaction effect of Cd input and water logging depth on Cd content and accumulation factor was significant. These results suggest that WSRS caused short-term heavy metal input and changes in water conditions affect wetland vegetation growth and heavy metal absorption in the downstream estuary.

Individual and combined contamination of oxytetracycline and cadmium inhibited nitrification by inhibiting ammonia oxidizers

INTRODUCTION

The large-scale development of animal husbandry and industrialization lead to more and more serious co-contamination from heavy metals and antibiotics in soils. Ecotoxic effects of residues from antibiotics and heavy metals are of increasing concern.

MATERIALS AND METHODS

In this study, oxytetracycline (OTC) and cadmium (Cd) were selected as target pollutants to evaluate the individual and combined effects on nitrification process using four different soil types sampled from North to South China through a 56-day incubation experiment.

RESULTS AND DISCUSSION

The results demonstrated that the contaminations of OTC and Cd, especially combined pollution had significant inhibitory effects on net nitrification rates (NNRs) as well as on AOA and AOB abundance. The toxic effects of contaminants were greatly enhanced with increasing OTC concentration. AOB was more sensitive than AOA to exogenous contaminants. And the interaction effects of OTC and Cd on ammonia oxidizers were mainly antagonistic. Furthermore, Cd contaminant (with or without OTC) had indirect effects on nitrification activity via inhibiting mineral N and AOA/AOB, while OTC alone indirectly inhibited nitrification activity by inhibiting ammonia oxidizers. The results could provide theoretical foundation for exploring the eco-environmental risks of antibiotics and heavy metals, as well as their toxic effects on nitrification processes.

Insights on Cadmium Removal by Bioremediation: The Case of Haloarchaea

Although heavy metals are naturally found in the environment as components of the earth’s crust, environmental pollution by these toxic elements has increased since the industrial revolution. Some of them can be considered essential, since they play regulatory roles in different biological processes; but the role of other heavy metals in living tissues is not clear, and once ingested they can accumulate in the organism for long periods of time causing adverse health effects. To mitigate this problem, different methods have been used to remove heavy metals from water and soil, such as chelation-based processes. However, techniques like bioremediation are leaving these conventional methodologies in the background for being more effective and eco-friendlier. Recently, different research lines have been promoted, in which several organisms have been used for bioremediation approaches. Within this context, the extremophilic microorganisms represent one of the best tools for the treatment of contaminated sites due to the biochemical and molecular properties they show. Furthermore, since it is estimated that 5% of industrial effluents are saline and hypersaline, halophilic microorganisms have been suggested as good candidates for bioremediation and treatment of this kind of samples. These microorganisms, and specifically the haloarchaea group, are of interest to design strategies aiming the removal of polluting compounds due to the efficiency of their metabolism under extreme conditions and their significant tolerance to highly toxic compounds such as heavy metals, bromate, nitrite, chlorate, or perchlorate ions. However, there are still few trials that have proven the bioremediation of environments contaminated with heavy metals using these microorganisms. This review analyses scientific literature focused on metabolic capabilities of haloarchaea that may allow these microbes to tolerate and eliminate heavy metals from the media, paying special attention to cadmium. Thus, this work will shed light on potential uses of haloarchaea in bioremediation of soils and waters negatively affected by heavy metals, and more specifically by cadmium.