Application of environmental DNA for assessment of contamination downstream of a legacy base metal mine

CaAl-Layered Double Hydroxides-Modified Biochar Composites Mitigate the Toxic Effects of Cu and Pb in Soil on Pea Seedlings

Compound contamination of soil with heavy metals copper (Cu) and lead (Pb) triggered by mining development has become a serious problem. To solve this problem, in this paper, corncob kernel, which is widely available and inexpensive, was used as the raw material of biochar and modified by loading CaAl-layered double hydroxides to synthesize biochar-loaded CaAl-layered double hydroxide composites (CaAl-LDH/BC). After soil remediation experiments, either BC or CaAl-LDH/BC can increase soil pH, and the available phosphorus content and available potassium content in soil. Compared with BC, CaAl-LDH/BC significantly reduced the available content of Cu and Pb in the active state (diethylenetriaminepentaacetic acid extractable state) in the soil, and the passivation rate of Cu and Pb by a 2% dosage of CaAl-LDH/BC reached 47.85% and 37.9%, respectively. CaAl-LDH/BC can significantly enhance the relative abundance of beneficial microorganisms such as Actinobacteriota, Gemmatimonadota, and Luteimonas in the soil, which can help to enhance the tolerance and reduce the enrichment ability of plants to heavy metals. In addition, it was demonstrated by pea seedling (Pisum sativum L.) growing experiments that CaAl-LDH/BC increased plant fresh weight, root length, plant height, catalase (CAT) activity, and protein content, which promoted the growth of the plant. Compared with BC, CaAl-LDH/BC significantly reduced the Cu and Pb contents in pea seedlings, in which the Cu and Pb contents in pea seedlings were reduced from 31.97 mg/kg and 74.40 mg/kg to 2.92 mg/kg and 6.67 mg/kg, respectively, after a 2% dosage of CaAl-LDH/BC, which was a reduction of 90.84% and 91.03%, respectively. In conclusion, compared with BC, CaAl-LDH/BC improved soil fertility and thus the plant growth environment, and also more effectively reduced the mobility of heavy metals Cu and Pb in the soil to reduce the enrichment of Cu and Pb by plants.

Exploitation of environmental DNA (eDNA) for ecotoxicological research: A critical review on eDNA metabarcoding in assessing marine pollution

The rise in worldwide population has led to a noticeable spike in the production, consumption, and transportation of energy and food, contributing to elevated environmental pollution. Marine pollution is a significant global environmental issue with ongoing challenges, including plastic waste, oil spills, chemical pollutants, and nutrient runoff, threatening marine ecosystems, biodiversity, and human health. Pollution detection and assessment are crucial to understanding the state of marine ecosystems. Conventional approaches to pollution evaluation usually represent laborious and prolonged physical and chemical assessments, constraining their efficacy and expansion. The latest advances in environmental DNA (eDNA) are valuable methods for the detection and surveillance of pollution in the environment, offering enhanced sensibility, efficacy, and involvement. Molecular approaches allow genetic information extraction from natural resources like water, soil, or air. The application of eDNA enables an expanded evaluation of the environmental condition by detecting both identified and unidentified organisms and contaminants. eDNA methods are valuable for assessing community compositions, providing indirect insights into the intensity and quality of marine pollution through their effects on ecological communities. While eDNA itself is not direct evidence of pollution, its analysis offers a sensitive tool for monitoring changes in biodiversity, serving as an indicator of environmental health and allowing for the indirect estimation of the impact and extent of marine pollution on ecosystems. This review explores the potential of eDNA metabarcoding techniques for detecting and identifying marine pollutants. This review also provides evidence for the efficacy of eDNA assessment in identifying a diverse array of marine pollution caused by oil spills, harmful algal blooms, heavy metals, ballast water, and microplastics. In this report, scientists can expand their knowledge and incorporate eDNA methodologies into ecotoxicological research.

eDNA metabarcoding reveals shifts in sediment eukaryote communities in a metal contaminated estuary

Metal contamination is a global issue impacting biodiversity in urbanised estuaries. Traditional methods to assess biodiversity are time consuming, costly and often exclude small or cryptic organisms due to difficulties with morphological identification. Metabarcoding approaches have been increasingly recognised for their utility in monitoring, however studies have focused on freshwater and marine systems despite the ecological significance of estuaries. We targeted estuarine eukaryote communities within the sediments of Australia's largest urbanised estuary, where a history of industrial activity has resulted in a metal contamination gradient. We identified specific eukaryote families with significant correlations with bioavailable metal concentrations, indicating sensitivity or tolerance to specific metals. While polychaete families Terebellidae and Syllidae demonstrated tolerance to the contamination gradient, members of the meio- and microfaunal communities including diatoms, dinoflagellates and nematodes displayed sensitivities. These may have high value as indicators but are frequently missed in traditional surveys due to sampling limitations.

Characterizing the spatial distributions of soil biota at a legacy base metal mine using environmental DNA

Characterizing the distribution of biota in response to contaminants is a critical element of site risk assessments. In this study we investigated the spatial distributions of biota and soil chemistry data in surface soil from Sunny Corner, a legacy base metal sulfide mine, Australia. Our results showed that copper (Cu), zinc (Zn), arsenic (As) and lead (Pb) in the surface soil exceeded Australian national soil quality guidelines and posed risks to the environment. Environmental (e)DNA metabarcoding of prokaryote and eukaryote composition confirmed the suggestion of environmental risk posed by these elements collectively explaining 72.9 % and 60.5 % of the total variation in the composition of soil prokaryotes and eukaryotes, respectively. Prokaryotic taxa from the phyla Gemmatimonadetes, Verrucomicrobia and Deinococcus-Thermus showed similar spatial patterns to As and Pb, and were positively correlated. Eukaryotic taxa from the phylum Chlorophyta had similar positive correlations with As and Pb in the soil. In contrast, Amoebozoa and Cercozoa, were sensitive to metals and metalloids, having higher relative abundances in soils with lower concentrations of contaminants. Our study shows that metabarcoding is a promising ecological approach for rapid, large scale assessment of contaminated and potentially impacted sites.

Impact assessment of ephemeral discharge of contamination downstream of two legacy base metal mines using environmental DNA

Mining and processing metalliferous ores can degrade the environment well beyond the footprint of the mine, particularly where on-site containment and post-mining remediation has been insufficient to prevent releases of solid and aqueous mine wastes. In this study, we investigated the potential of sediment and water chemistry coupled with environmental (e)DNA metabarcoding to evaluate discrete and cumulative ecological impacts of two legacy base metal (copper (Cu), zinc (Zn), lead (Pb)) mines (Peelwood and Cordillera) which discharge metals via ephemeral tributaries into perennial Peelwood Creek. Although the two mine streams exceeded Australian guidelines for sediment and freshwater quality for Cu, Zn and Pb, Peelwood Creek had relatively low sediment and water metal concentrations, suggesting a low potential for environmental toxicity. Although sediment and water chemistry defined the extent of biological impacts, metabarcoding showed that Peelwood and Cordillera mines had discrete impacts and Peelwood mine was the main source of contamination of Peelwood Creek. Metabarcoding showed that prokaryotes can be good indicators of metal contamination whereas eukaryotes did not reflect contamination impacts in Peelwood Creek. Metabarcoding results showed that benthic communities downstream of Cordillera mine were less impacted than those below Peelwood mine, suggesting that Peelwood mine should be considered for further remediation.