Sediment geochemistry of streams draining abandoned lead / zinc mines in central Wales: the Afon Twymyn

Purpose Despite the decline of metal mining in the UK during the early 20th century, a substantial legacy of heavy metal contamination persists in river channel and floodplain sediments. Poor sediment quality is likely to impede the achievement of ’good’ chemical and ecological status for surface waters under the European Union Water Framework Directive. This paper examines the environmental legacy of the Dylife lead/zinc mine in the central Wales mining district. Leachable heavy metal concentrations in the bed sediments of the Afon Twymyn are established and the geochemical partitioning, potential mobility and bioavailability of sediment-associated heavy metals are established. Materials and methods Sediment samples were collected from the river bed and dry-sieved into two size fractions (<63 μm and 64–2,000 μm). The fractionated samples were then subjected to a sequential extraction procedure to isolate heavy metals (Pb, Zn, Cu, Cd, Fe, Mn) in three different geochemical phases. Sediment samples were then analysed for heavy metals using ICP-AES. Results and discussion The bed sediment of the Afon Twymyn is grossly polluted with heavy metals. Within the vicinity of the former mine, Pb concentrations are up to 100 times greater than levels reported to have deleterious impacts on aquatic ecology. Most heavy metals exist in the most mobile easily exchangeable and carbonate-bound geochemical phases, potentially posing serious threats to ecological integrity and constituting a significant, secondary, diffuse source of pollution. Metal concentrations decrease sharply downstream of the former mine, although there is a gradual increase in the proportion of readily extractable Zn and Cd. Conclusions Implementation of sediment quality guidelines is important in order to achieve the aims of the Water Framework Directive. Assessments of sediment quality should include measurements of background metal concentrations, river water physico-chemistry and, most importantly, metal mobility and potential bioavailability. Uniformity of sediment guidelines throughout Europe and flexibility of targets with regard to the most heavily contaminated mine sites are recommended

Risks of mining to salmonid-bearing watersheds

Mining provides resources for people but can pose risks to ecosystems that support cultural keystone species. Our synthesis reviews relevant aspects of mining operations, describes the ecology of salmonid-bearing watersheds in northwestern North America, and compiles the impacts of metal and coal extraction on salmonids and their habitat. We conservatively estimate that this region encompasses nearly 4000 past producing mines, with present-day operations ranging from small placer sites to massive open-pit projects that annually mine more than 118 million metric tons of earth. Despite impact assessments that are intended to evaluate risk and inform mitigation, mines continue to harm salmonid-bearing watersheds via pathways such as toxic contaminants, stream channel burial, and flow regime alteration. To better maintain watershed processes that benefit salmonids, we highlight key windows during the mining governance life cycle for science to guide policy by more accurately accounting for stressor complexity, cumulative effects, and future environmental change.This review is based on an October 2019 workshop held at the University of Montana Flathead Lake Biological Station (more information at https://flbs.umt.edu/ newflbs/research/working-groups/mining-and-watersheds/). We thank E. O’Neill and other participants for valuable contributions. A. Beaudreau, M. LaCroix, P. McGrath, K. Schofield, and L. Brown provided helpful reviews of earlier drafts. Three anonymous reviewers provided thoughtful critiques that greatly improved the manuscript. The views expressed in this article are those of the authors and do not necessarily represent the views or policies of the U.S. Environmental Protection Agency. Our analysis comes from a western science perspective and hence does not incorporate Indigenous knowledge systems. We acknowledge this gap and highlight that the lands and waters we explore in this review have been stewarded by Indigenous Peoples for millennia and continue to be so. Funding: The workshop was cooperatively funded by the Wilburforce Foundation and The Salmon Science Network funded by the Gordon and Betty Moore Foundation. Author contributions: C.J.S. led the review process, writing, and editing. C.J.S. and E.K.S. co-organized the workshop. E.K.S. and J.W.M. extensively contributed to all aspects of the review conceptualization, writing, and editing. A.R.W., S.A.N., J.L.E., D.M.C., S.L.O., R.L.M., F.R.H., D.C.W., and J.W. significantly contributed to portions of the review conceptualization, writing, and editing. J.C., M.Ca., M.Co., C.A.F., G.K., E.D.L., R.M., V.M., J.K.M., M.V.M., and N.S. provided writing and editing and are listed alphabetically. Competing interests: The authors declare that they have no competing interests. Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials.Ye

Utilization of Cofactor Binding Energy for Enzyme Catalysis: Formate Dehydrogenase-Catalyzed Reactions of the Whole NAD Cofactor and Cofactor Pieces

The pressure to optimize enzymatic rate accelerations has driven the evolution of the induced-fit mechanism for enzyme catalysts where the binding interactions of nonreacting phosphodianion or adenosyl substrate pieces drive enzyme conformational changes to form protein substrate cages that are activated for catalysis. We report the results of experiments to test the hypothesis that utilization of the binding energy of the adenosine 5′-diphosphate ribose (ADP-ribose) fragment of the NAD cofactor to drive a protein conformational change activates Candida boidinii formate dehydrogenase (CbFDH) for catalysis of hydride transfer from formate to NAD+. The ADP-ribose fragment provides a >14 kcal/mol stabilization of the transition state for CbFDH-catalyzed hydride transfer from formate to NAD+. This is larger than the ca. 6 kcal/mol stabilization of the ground-state Michaelis complex between CbFDH and NAD+ (KNAD = 0.032 mM). The ADP, AMP, and ribose 5′-phosphate fragments of NAD+ activate CbFDH for catalysis of hydride transfer from formate to nicotinamide riboside (NR). At a 1.0 M standard state, these activators stabilize the hydride transfer transition states by ≈5.5 (ADP), 5.5 (AMP), and 4.4 (ribose 5′-phosphate) kcal/mol. We propose that activation by these cofactor fragments is partly or entirely due to the ion-pair interaction between the guanidino side chain cation of R174 and the activator phosphate anion. This substitutes for the interaction between the α-adenosyl pyrophosphate anion of the whole NAD+ cofactor that holds CbFDH in the catalytically active closed conformation