Inadequate abandonment of copper mine tailings under semiarid Mediterranean climate type conditions has posed important environmental risks in Chile due to wind and rain erosion. There are cost-effective technologies for tailings stabilization such as phytostabilization. However, this technology has not been used in Chile yet. This study evaluated in a greenhouse assay the efficacy of biosolids, lime, and a commercial mycorrhiza to improve adverse conditions of oxidized Cu mine tailings for adequate establishment and grow of Lolium perenne L. var nui. Chemical characterization of experimental substrates and pore water samples were performed; plant density, biomass production, chlorophyll content, and metal content in shoots was evaluated in rye grass plants after an eight-week growth period. Results showed that neutralization of tailings and superficial application of biosolids increased both aerial biomass production and chlorophyll content of rye grass. Increased Cu solubilization and translocation to shoots occurred after biosolids application (mixed), particularly on unlimed tailings, due to formation of soluble organometallic complexes with dissolved organic carbon (DOC) which can be readily absorbed by plant roots. Positive effects of mycorrhizal inoculation on rye grass growth were restricted to treatments with superficial application of biosolids, probably due to Cu toxicity effects on commercial mycorrhiza used (Glomulus intraradices).
The objective of this study was to assess the predictive capacity of the biotic ligand model (BLM) for acute copper toxicity to daphnids as applied to a number of freshwaters from Chile and to synthetic laboratory-prepared waters. Thirty-seven freshwater bodies were sampled, chemically characterized, and used to determine the copper concentration associated with the 50% of mortality (LC50) for Daphnia magna, Daphnia pulex, and Daphnia obtusa (native to Chile). The data were then used to run three versions of the acute copper BLM, and the predicted LC50s were compared to the observed ones. The same was done with synthetic assay media at various hardness and dissolved organic carbon (DOC) levels. The BLM versions differed in the affinity constants for some biotic ligand-ion pairs, stability constants for inorganic Cu complexes, and assumptions regarding Cu binding to DOC. All three versions showed a high degree of predictive performance, mostly within a twofold range of observed toxicity values. The D. obtusa data set was used to compare water quality criteria (WQC) derived from the observed toxicity values with those derived from either the BLM or the U.S. Environmental Protection Agency (U.S. EPA) procedure. For most low DOC waters, the three procedures generated similar WQCs. For the high-DOC waters, the EPA-derived criteria were significantly lower, that is, greatly overprotective. The results are also discussed in terms of the validation of the BLM for regulatory use.
A better understanding of exposure to and effects of copper-rich pollutants in soils is required for accurate environmental risk assessment of copper. A greenhouse experiment was conducted to study copper bioavailability and bioaccumulation in agricultural soils spiked with different types of copper-rich mine solid wastes (copper ore, tailing sand, smelter dust, and smelter slag) and copper concentrate. A copper salt (copper sulfate, CuSO4) that frequently is used to assess soil copper bioavailability and phytotoxicity also was included for comparison. Results showed that smelter dust, tailing sand, and CuSO4 are more likely to be bioavailable and, thus, toxic to plants compared with smelter slag, concentrate, and ore at equivalent total copper concentrations. Differences may be explained by intrinsic differences in copper solubilization from the source materials, but also by their capability to decrease soil pH (confounding effect). The copper toxicity and bioaccumulation in plants also varied according to soil physicochemical characteristics (e.g., pH and total organic carbon) and the available levels of plant nutrients, such as nitrogen, phosphorus, and potassium. Chemistry/mineralogy of mine materials, soil/pore-water chemistry, and plant physiological status thus should be integrated for building adequate models to predict phytotoxicity and environmental risk of copper.
The objective of the present study was to assess the predictive capacity of the acute Cu biotic ligand model (BLM) as applied to chronic Cu toxicity to Daphnia magna in freshwaters from Chile and synthetic laboratory-prepared waters. Samples from 20 freshwater bodies were taken, chemically characterized, and used in the acute Cu BLM to predict the 21-d chronic Cu toxicity for D. magna. The half-maximal effective concentration (EC50) values, determined using the Organisation for Economic Co-operation and Development (OECD) 21-d reproduction test (OECD Method 211), were compared with the BLM simulated EC50 values. The same EC50 comparison was performed with the results of 19 chronic tests in synthetic media, with a wide range of hardness and alkalinity and a fixed 2 mg/L dissolved organic carbon (DOC) concentration. The acute BLM was modified only by adjustment of the accumulation associated with 50% of an effect value (EA50). The modified BLM model was able to predict, within a factor of two, 95% of the 21-d EC50 and 89% of the 21-d half-maximal lethal concentrations (LC50) in natural waters, and 100% of the 21-d EC50 and 21-d LC50 in synthetic waters. The regulatory implications of using a slightly modified version of an acute BLM to predict chronic effects are discussed.
Pollution of soil with mine wastes results in both Cu enrichment and soil acidification. This confounding effect may be very important in terms of phytotoxicity, because pH is a key parameter influencing Cu solubility in soil solution. Laboratory toxicity tests were used to assess the effect of acidification by acidic mine wastes on Cu solubility and on root elongation of barley (Hordeum vulgare L.). Three contrasting substrates (two soils and a commercial sand) and two acidic, Cu-rich mine wastes (oxidized tailings [OxT] and smelter dust [SmD]) were selected as experimental materials. Substrates were spiked with a fixed amount of either SmD or OxT, and the pH of experimental mixtures was then modified in the range of 4.0 to 6.0 and 7.0 using PIPES (piperazine-1,4-bis(2-ethanesulfonic acid)), MES (2-(N-morpholino)ethanesulfonic acid), and MOPS (3-(N-Morpholino)-propanesulfonic acid) buffers. Chemical (pore-water Cu and pH) and toxicological (root length of barley plants) parameters were determined for experimental mixtures. Addition of SmD and OxT to substrates resulted in acidification (0.11-1.16 pH units) and high levels of soluble Cu and Zn. Neutralization of experimental mixtures with MES (pH 6.0) and MOPS (pH 7.0) buffers resulted in a marked decrease in soluble Cu and Zn, but the intensity of the effect was substrate-dependent. Adjustment of soil pH above the range normally considered to be toxic to plants (pH in water extract, > 5.5) significantly reduced metal toxicity in barley, but phytotoxicity was not completely eliminated. The present results stress the importance of considering confounding effects on derivation of toxicity thresholds to plants when using laboratory phytotoxicity tests.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.