Ecological risk assessment of boreal sediments affected by metal mining: Metal geochemistry, seasonality, and comparison of several risk assessment methods

Abstract

The mining industry is a common source of environmental metal emissions, which cause long-lasting effects in aquatic ecosystems. Metal risk assessment is challenging due to variations in metal distribution, speciation, and bioavailability. Therefore, seasonal effects must be better understood, especially in boreal regions in which seasonal changes are large. We sampled 4 Finnish lakes and sediments affected by mining for metals and geochemical characteristics in autumn and late winter, to evaluate seasonal changes in metal behavior, the importance of seasonality in risk assessment, and the sensitivity and suitability of different risk assessment methods. We compared metal concentrations in sediment, overlying water, and porewater against environmental quality guidelines (EQGs). We also evaluated the toxicity of metal mixtures using simultaneously extracted metals and an acid volatile sulfides (SEM-AVS) approach together with water quality criteria (US Environmental Protection Agency equilibrium partitioning benchmarks). Finally, site-specific risks for 3 metals (Cu, Ni, Zn) were assessed using 2 biotic ligand models (BLMs). The metal concentrations in the impacted lakes were elevated. During winter stratification, the hypolimnetic O2 saturation levels were low (<6%) and the pH was acidic (3.5-6.5); however, abundant O2 (>89%) and neutral pH (6.1-7.5) were found after the autumnal water overturn. Guidelines were the most conservative benchmark for showing an increased risk of toxicity in the all of the lakes. The situation remained stable between seasons. On the other hand, SEM-AVS, equilibrium partition sediment benchmarks (ESBs), and BLMs provided a clearer distinction between lakes and revealed a seasonal variation in risk among some of the lakes, which evidenced a higher risk during late winter. If a sediment risk assessment is based on the situation in the autumn, the overall risk may be underestimated. It is advisable to carry out sampling and risk assessment during periods in which metals are assumed to be the most environmentally harmful. Integr Environ Assess Manag 2016;12:759-771. © 2015 SETAC.

Ecotoxicity assessment of boreal lake sediments affected by metal mining: Sediment quality triad approach complemented with metal bioavailability and body residue studies

“…We studied four, metal-contaminated lakes in Finland. We complemented the traditional SQT approach (1-3) with additional, applied SQT methods (4-5) as following: (1) Analysis of sediment chemistry, conducted in our earlier study (Väänänen et al, 2016), (2) benthic community structure analyses, where the total number of organisms and the abundancy of specimen were studied, (3) a selection of toxicity tests (luminescence bacteria Vibrio fischeri, oligochaete Lumbriculus variegatus, snail Lymnaea stagnalis, and an early warning behavioral test with midge Chironomus riparius), (4) metal bioavailability from our previous study (Väänänen et al 2016) and ( 5) metal bioaccumulation as metal body residues in field-collected fish and chironomids…”

“…(previously Talvivaara Mine) next to Lake LJ, which quarries Ni, Cu, Zn and Co. Lake SJ is located next to the Outokumpu Mine, where Cu mining activities ceased in the 1980s. Thorough chemical analysis of these lake sediments was conducted in our earlier study and the metal concentrations in these lake sediments were elevated for Ni (28-204 mg/kg), Zn (168-863 mg/kg), Cu (19-248 mg/kg) and As (6-53 mg/kg), analyzed by ICP-MS (Table 1) (Väänänen et al, 2016). Several sediments were used as references for the toxicity tests.…”

“…In addition to bulk sediments, pore water samples were tested. Pore waters were extracted using Rhizon samplers as described by Väänänen et al (2016). The toxicity tests were performed as with the sediment samples, but without the initial dilution step.…”

“…The chironomid samples were rinsed with MilliQ water, weighed and dried in an oven (+40 °C) overnight, after which they were analyzed with ICP-MS (Inductively coupled plasma mass spectrometry, SGS Inspector Services, Finland). As, Cu, Ni and Zn were included for this study, since they were earlier identified as the metal species most likely to induce adverse effects in these lakes (Väänänen et al, 2016). Correlations between metal concentrations in biota, pore water, overlying water and sediment were tested with the Pearson's correlation (GraphPad Prism 5).…”

“…Bio-met, version 2.3 (Väänänen et al, 2016). This BLM evaluates the bioavailability of Cu, Ni and Zn.…”