The protection of wildlife from mortality: hypothesis and results for risk assessment

Environmental challenges related to cyanidation in Central American gold mining; the Remance mine (Panama)

Mine tailings are a potential source of environmental pollution because they typically contain potentially toxic elements (PTEs) and the residue of chemical compounds used during extraction processes. The Remance gold mine (NW Panama) is a decommissioned mine with mining activity records dating from the 1800s and several periods of abandonment. Very little remediation work has been performed, and waste is exposed to climatic conditions. This study aimed to evaluate the PTEs and cyanide contents in mine waste after mining operations ceased some 20 years ago, and to evaluate the degree of pollution and the environmental risks they pose with the use of the Pollution Load Index (PLI) and the Ecological Risk Index (RI). Although the total cyanide (T-CN) concentration (1.4-1.9 mg kg^-1) found in most of the study area falls within the limits of gold mining tailing values for American sites (1.5-23 mg kg^-1), it is worth noting that the values of the tailings of the last used mining operation exceed it (25.2-518 mg kg^-1) and persist at the site. The PLI and RI suggest that the tailings from the mine and mine gallery sediments represent a source of pollution for soils and surrounding areas given their high content of PTEs (As, Cu, Sb, Hg) and T-CN, which pose serious ecological risks for biota. Therefore, it is necessary to draw up a remediation plan for this area.

Effects of physicochemical properties of Au cyanidation tailings on cyanide microbial degradation

The initial cyanide (CN^-) concentration and amount of co-contaminants in GCTs can inhibit bacterial growth and reduce the CN^--degrading ability of bacteria. Several microorganisms can biotransform a wide range of organic and inorganic industrial contaminants into nontoxic compounds. However, active enzymatic CN^- metabolism processes are mostly constrained by the physical and chemical characteristics of GCTs. High concentrations of toxic metal co-contaminants, such as, Pb, and Cr, and factors, such as pH, temperature, and oxygen concentration create oxidative stress and limit the CN^--degrading potential of cyanotrophic strains. The effects of such external and internal factors on the CN^--degrading ability of bacteria hinder the selection of suitable microorganisms for CN^- biodegradation. Therefore, understanding the effects of the physicochemical properties of GCTs on cyanobacteria strains can help identify suitable microbes and favorable environmental conditions to promote microbial growth and can also help design efficient CN^- biodegradation processes. In this review, we present a detailed analysis of the physicochemical properties of GCTs and their effects on microbial CN^- degradation.

Impact of anthropogenic pressures on wild mammals of Northern Portugal

Background and Aim:

Wild mammals are among the most threatened species of the world in large part due to human activity. In this work, we used the method of partial least squares-path modeling associated with a geographic information system to analyze the impact of anthropogenic pressures on the mortality of wild mammals.

Materials and Methods:

We collected the data related to the cause of death of native wild mammals admitted to the Wildlife Rehabilitation Centre of Parque Biológico de Gaia in Northern Portugal, during 10 years (2008-2017).

Results:

A total of 359 animals from 42 municipalities (rural and urban areas) were included in the study. The main cause of death was of traumatic origin. From the anthropogenic pressures included in the study, water reservoirs, small companies, and residential buildings were the ones that contributed the most to increase the mortality of traumatic and non-traumatic origin. This relation of cause-effect (mortality-anthropogenic pressures) was supported by the high coefficients of determination obtained (R² > 0.8).

Conclusion:

The present results allow a general view on the reality of mammal’s mortality in Northern Portugal. Furthermore, it could also constitute a valuable tool for the conservation of wild mammals in those areas.

Determination and detoxification of cyanide in gold mine tailings: A review

Cyanide is among the most toxic chemicals widely employed in the cyanidation process to leach precious minerals, such as gold and silver, by the minerals processing companies worldwide. This present article reviews the determination and detoxification of cyanide found in gold mine tailings. Most of the cyanide remains in the solution or the slurries after the cyanidation process. The cyanide species in the gold tailings are classified as free cyanide, weak acid dissociation, and metallocyanide complexes. Several methods, such as colorimetric, titrimetric, and electrochemical, have been developed to determine cyanide concentrations in gold mine effluents. Application of physical, natural, biological, and chemical methods to detoxify cyanide to a permissible limit (50 mg L^-1) can be achieved when the chemical compositions of cyanide (type of species) present in the tailings are known. The levels of cyanide concentration determine the impact it will have on the environment.

High levels of activity of bats at gold mining water bodies: implications for compliance with the International Cyanide Management Code

Wildlife and livestock are known to visit and interact with tailings dam and other wastewater impoundments at gold mines. When cyanide concentrations within these water bodies exceed a critical toxicity threshold, significant cyanide-related mortality events can occur in wildlife. Highly mobile taxa such as birds are particularly susceptible to cyanide toxicosis. Nocturnally active bats have similar access to uncovered wastewater impoundments as birds; however, cyanide toxicosis risks to bats remain ambiguous. This study investigated activity of bats in the airspace above two water bodies at an Australian gold mine, to assess the extent to which bats use these water bodies and hence are at potential risk of exposure to cyanide. Bat activity was present on most nights sampled during the 16-month survey period, although it was highly variable across nights and months. Therefore, despite the artificial nature of wastewater impoundments at gold mines, these structures present attractive habitats to bats. As tailings slurry and supernatant pooling within the tailings dam were consistently well below the industry protective concentration limit of 50 mg/L weak acid dissociable (WAD) cyanide, wastewater solutions stored within the tailings dam posed a minimal risk of cyanide toxicosis for wildlife, including bats. This study showed that passively recorded bat echolocation call data provides evidence of the presence and relative activity of bats above water bodies at mine sites. Furthermore, echolocation buzz calls recorded in the airspace directly above water provide indirect evidence of foraging and/or drinking. Both echolocation monitoring and systematic sampling of cyanide concentration in open wastewater impoundments can be incorporated into a gold mine risk-assessment model in order to evaluate the risk of bat exposure to cyanide. In relation to risk minimisation management practices, the most effective mechanism for preventing cyanide toxicosis to wildlife, including bats, is capping the concentration of cyanide in tailings discharged to open impoundments at 50 mg/L WAD.

Hypersalinity reduces the risk of cyanide toxicosis to insectivorous bats interacting with wastewater impoundments at gold mines

Wildlife and livestock that ingest bioavailable cyanide compounds in gold mining tailings dams are known to experience cyanide toxicosis. Elevated levels of salinity in open impoundments have been shown to prevent wildlife cyanide toxicosis by reducing drinking and foraging. This finding appears to be consistent for diurnal wildlife interacting with open impoundments, however the risks to nocturnal wildlife of cyanide exposure are unknown. We investigated the activity of insectivorous bats in the airspace above both fresh (potable to wildlife) and saline water bodies at two gold mines in the goldfields of Western Australian. During this study, cyanide-bearing solutions stored in open impoundments at both mine sites were hypersaline (range=57,000-295,000 mg/L total dissolved solids (TDS)), well above known physiological tolerance of any terrestrial vertebrate. Bats used the airspace above each water body monitored, but were more active at fresh than saline water bodies. In addition, considerably more terminal echolocation buzz calls were recorded in the airspace above fresh than saline water bodies at both mine sites. However, it was not possible to determine whether these buzz calls corresponded to foraging or drinking bouts. No drinking bouts were observed in 33 h of thermal video footage recorded at one hypersaline tailings dam, suggesting that this water is not used for drinking. There is no information on salinity tolerances of bats, but it could be assumed that bats would not tolerate salinity in drinking water at concentrations greater than those documented as toxic for saline-adapted terrestrial wildlife. Therefore, when managing wastewater impoundments at gold mines to avoid wildlife mortalities, adopting a precautionary principle, bats are unlikely to drink solutions at salinity levels ≥50,000 mg/L TDS.

Factors influencing the risk of wildlife cyanide poisoning on a tailings storage facility in the Eastern Goldfields of Western Australia

Patterns of wildlife visitation and interaction with cyanide-bearing tailings slurry and solutions at the Fimiston tailings storage facility (TSF) have been reported in a previously published ecological study. The above-mentioned findings are extended in this paper by the examination of additional wildlife survey data, along with process water chemistry data collected during the same study period. Analysis of the combined results revealed that the primary wildlife protective mechanism in operation was effective management of tailings cyanide concentration. Nevertheless, tailings discharge concentration exceeded the industry standard wildlife protective limit of 50mg/L weak acid dissociable (WAD) cyanide episodically during the study period. Wildlife that interacted with habitats close to the spigot outlet during brief periods of increased discharge concentration were likely to have been exposed to bioavailable cyanide at concentrations greater than the industry standard protective limit. However, no wildlife deaths were recorded. These results appear to support the hypothesis that hypersalinity of process solutions (unique to the Kalgoorlie district of Western Australia) and a lack of aquatic food resources represent secondary protective mechanisms that operated to prevent cyanide-related wildlife mortality during the project. The proposed protective mechanisms are discussed in the context of their potential application as proactive management procedures to minimise wildlife exposure to cyanide.