Which distribution to choose for deriving a species sensitivity distribution? Implications from analysis of acute and chronic ecotoxicity data.

Species sensitivity distributions (SSDs) estimated by fitting a statistical distribution to ecotoxicity data are indispensable tools used to derive the hazardous concentration for 5 % of species (HC5) and thereby a predicted no-effect concentration in environmental risk assessment. Whereas various statistical distributions are available for SSD estimation, the fundamental question of which statistical distribution should be used has received limited systematic analysis. We aimed to address this knowledge gap by applying four frequently used statistical distributions (log-normal, log-logistic, Burr type III, and Weibull distributions) to acute and chronic SSD estimation using aquatic toxicity data for 191 and 31 chemicals, respectively. Based on the differences in the corrected Akaike's information criterion (AICc) as well as visual inspection of the fitting of the lower tails of SSD curves, the log-normal SSD was generally better or equally good for the majority of chemicals examined. Together with the fact that the ratios of HC5 values of other alternative SSDs to those of log-normal SSDs generally fell within the range 0.1-10, our findings indicate that the log-normal distribution can be a reasonable first candidate for SSD derivation, which does not contest the existing widespread use of log-normal SSDs.

Effect of hardware removal and second-look arthroscopy after open-wedge high tibial osteotomy.

INTRODUCTION: Open-wedge high tibial osteotomy (OWHTO) is the standard and safe procedure for medial compartment osteoarthritis. Although hardware removal (HWR) is performed after post-OWHTO bone union, the effects of HWR on OWHTO have been rarely reported. We hypothesised that HWR would improve range of motion (ROM) and implant-related complications. Thus, this study aimed to investigate the effects of HWR on postoperative ROM, the Japan Orthopaedic Association (JOA) score/visual analogue scale (VAS) score and hardware-related complications after OWHTO. METHODS: Patients who underwent OWHTO between January 2016 and June 2018 and HWR were retrospectively reviewed. To perform OWHTO, locking plates and prosthetic bone were used to achieve optimal stabilisation of biplanar osteotomy. HWR was performed after a second-look arthroscopy through the previous skin incision. For clinical evaluation, the JOA score, VAS score, and ROM were assessed before and 1 year after HWR using the Wilcoxon rank test. Logistic regression analysis was performed to identify the predictors of post-HWR improvement. RESULTS: Of 98 knees examined (91 patients), 80 (73 patients; 39 men and 34 women) were included. At the time of OWHTO, mean age was 64.0 ± 9.7 years and body mass index, 25.5 ± 3.1 kg/m2; Kellgren-Lawrence (KL) grade 1 was seen in 20 cases, KL-2 in 46, and KL-3 in 14. Mean periods between OWHTO and HWR were 13.4 ± 2.0 months, and 11.9 ± 1.2 months between HWR and evaluation. The JOA score and flexion angle significantly improved after HWR (The JOA score: p = 0.026 flexion angle: p < 0.001); however, the VAS score and extension angle did not (VAS score: p = 0.162, extension angle: p = 0.934). Hardware irritation was observed in four cases (5%), which improved after HWR. Logistic regression analysis revealed that lower preoperative KL grade and flexion angle were predictors of improvement after HWR [KL grade: p = 0.008; odds ratio 3.244, 95% confidence interval (CI) 1.350-7.794; flexion angle: p < 0.001; odds ratio 1.150, 95% CI 1.062-1.245]. CONCLUSION: HWR improves flexion angle, clinical outcomes and hardware-related complications after OWHTO. Preoperative KL grade and flexion angle are predictors of improvement after HWR in patients who have undergone OWHTO.

Good clinical outcomes and return to sports after hybrid closed-wedge high tibial osteotomy.

PURPOSE: This study aimed to investigate preoperative sports participation and postoperative clinical outcomes including a return to sports (RTS) after hybrid closed-wedge high tibial osteotomy (CWHTO) for medial compartment osteoarthritis of the knee. Characteristic of Hybrid CWHTO was defined as extra-articular lateral closed and medial open wedge osteotomy. METHODS: The patients who underwent hybrid CWHTO from January 2016 to December 2018 were retrospectively reviewed and divided them into sports and non-sports groups. The preoperative demographic and radiographic characteristics were compared in both groups. And the clinical outcomes including the Japanese Orthopaedic Association (JOA) score, visual analogue scale (VAS), Lysholm score, University of California at Los Angeles (UCLA) activity score, and RTS in the sports group were also investigated. Statistical analysis was performed for comparisons among the preoperative factors between the two groups. Influence of sports impact and bone union of fibular osteotomy was also statistically investigated for RTS. RESULTS: Of the 161 knees (129 patients; 46 males, 83 females), 20 knees (16 patients; 13 males, 3 females; 12.3%) belonged to sports group. Although there were no significant differences regarding the age and radiographic parameters, there were significant differences in the body mass index and proportion of males between both groups. The JOA, VAS, Lysholm, and UCLA activity scores significantly improved after surgery. RTS was 80% at a mean duration of 7.2 ± 3.1 months. RTS in the high-impact sports group was significantly lower than that in the low-impact sports group (high-impact 60% vs. low-impact 100%, p = 0.043). There was no significant difference in RTS regarding bone union after fibular osteotomy. CONCLUSION: The clinical outcomes including RTS were satisfactory in patients with hybrid CWHTO. LEVEL OF EVIDENCE: IV.

Mid-term results of medial open-wedge high tibial osteotomy based on radiological grading of osteoarthritis.

PURPOSE: To evaluate the mid-term results of medial open-wedge high tibial osteotomy (OWHTO) based on Kellgren-Lawrence (KL) grades. MATERIALS AND METHODS: We retrospectively evaluated clinical and radiographic outcomes of 93 patients (mean age 61.4 years, mean follow-up 64.2 months, 109 consecutive knees) who underwent OWHTO for medial compartment osteoarthritis (OA). KL grade was used to evaluate knee OA (KL-1 22 cases; KL-2, 51 cases; KL-3, 36 cases). The clinical outcomes were assessed using Japanese Orthopaedic Association (JOA) and Lysholm scores. Radiographic outcomes were assessed using pre- and post-operative mechanical axis percentage, femorotibial angle, medial proximal tibial angle, and joint line convergence angle. Hinge fracture frequency and OA progression were also evaluated based on KL grades. RESULTS: The JOA score improved significantly from 70.3 ± 14.9 to 96.2 ± 4.4, 64.1 ± 12.5 to 95.1 ± 5.1, and 68.6 ± 11.4 to 92.1 ± 6.1 in the KL-1, KL-2, and KL-3 groups, respectively. The JOA score in the KL-3 group was significantly lower than in the other groups. The Lysholm score improved significantly from 62.6 ± 8.8 to 97.7 ± 4.7, 62.1 ± 8.1 to 96.7 ± 4.2, and 59.2 ± 9.2 to 95.8 ± 4.6 in the KL-1, KL-2, and KL-3 groups, respectively. The post-operative Lysholm scores were not significantly different among the groups. There were significant differences in radiographic parameters pre-operatively, but not post-operatively, among the groups. Although there were no significant differences in hinge fracture frequency and OA progression, the KL-3 grade predicted OA progression on multivariate analysis. CONCLUSIONS: Mid-term results of OWHTO significantly improved. However, clinical score in the KL-3 group was lower than that in the KL-1 and KL-2 groups; radiological OA progression was a risk factor in KL-3.

Revisiting assessment factors for species sensitivity distributions as a function of sample size and variation in species sensitivity.

To use species sensitivity distributions (SSDs) for ecological risk assessment, there are various uncertainties, which require applying assessment factors (AFs) accordingly. This study aims to quantify the uncertainty of estimating statistical distributions. Given a management goal of protecting 95% of species, the concentration that affects 5% of the species (HC5) is estimated. Since the true concentration affecting 5% of the species (population HC5) is unknown, the estimated HC5 is divided by an AF to derive the predicted no-effect concentration (PNEC), which is set as the protection goal, to compensate for the deviation in the estimated HC5 from the population HC5. Although the deviation between these two HC5 values depends on the sample size and the variation in sensitivity (standard deviation of the distribution) among species, there has been little discussion of how to quantify the degree of uncertainty. By assuming that toxicity values are a random sample from a lognormal distribution, we mathematically analyzed the SSD to derive the magnitude of AF needed to achieve a given protection goal (as an example, the protection of 95% of species with a probability of 95%). We successfully derived an equation that explicitly relates the magnitude of AF to the sample size and the variation in species sensitivity, providing a new basis to statistically determine the magnitude of AF for ecological risk assessments.

Can We Reasonably Predict Chronic Species Sensitivity Distributions from Acute Species Sensitivity Distributions?

Estimation of species sensitivity distributions (SSDs) is an essential way to estimate the hazardous concentration for 5% of the species (HC5) and thus to derive a "safe" concentration. Here, we examined whether we can reasonably predict SSDs based on chronic no-observed-effect concentration or level (chronic SSDs) from SSDs based on acute median effective/lethal concentration (acute SSDs) by analyzing log-normal SSDs of 150 chemicals. Chronic SSD means were, on average, 10 times lower than acute SSD means. The standard deviations (SDs) of acute and chronic SSDs closely overlapped. Our detailed analysis suggests that the acute SSD SD can be used as an initial estimate of the chronic SSD SD if the number of tested species is ≥10. There were no significant differences in the ratios of chronic to acute SSD means or SDs among three different modes of action. The HC5 of chronic SSDs was, on average, 10 times lower than the acute SSD HC5. We suggest that multiplication of the acute HC5 by a factor of 0.1 is a defensible way to obtain a first approximation of the chronic HC5, particularly when relative ecological risks of chemicals are being evaluated. Further study is needed to develop methods for a more accurate estimation of chronic SSDs.

Coupling mixture reference models with DGT-perceived metal flux for deciphering the nonadditive effects of rare earth mixtures to wheat in soils.

The risk assessment of mixtures of rare earth elements (REEs) is hampered by a lack of fundamental understanding of their interactions in different soil types. Here, we assessed mixture interactions and toxicity to Triticum aestivum of Y and Ce in four different soils in relation to their bioavailability. Mixture toxicity was modelled by concentration addition (CA) and independent action (IA), in combination with different expressions of exposure: three equilibrium-based doses (total soil concentrations [M]tot, free ion activity in soil solution {M3+}, and the fraction (f) of metal ions bound to the biotic ligands (BLs)) and one kinetically controlled dose ([M]flux) metrics. Upon single exposure, REE toxicity was increasingly better described when using exposure expressions based on deepened understanding of their bioavailability: [M]flux > f > {M3+} > [M]tot. The mixture analyses based on [M]tot and {M3+} displayed deviations from additivity depending on the soil type. With the parameters derived from single exposures, the BLM approach gave better predictions of mixture toxicity (R2 ~ 0.70) than when using CA and IA based on either [M]tot or {M3+} (R2 < 0.64). About 30% of the variance in toxicity remained unexplained, challenging the view that the free metal ion is the main bioavailable form under the BLM framework based on thermodynamic equilibrium. Toxicity was best described when accounting for changes in the size of the labile metal pool by using a kinetically controlled dose metric (R2 ~ 0.80). This suggests that dynamic bioavailability analysis could provide a robust basis for modeling and reconciling the interplays and toxicity of metal mixtures in different soils.

Does a sum of toxic units exceeding 1 imply adverse impacts on macroinvertebrate assemblages? A field study in a northern Japanese river receiving treated mine discharge.

In ecological risk assessment, sum-of-toxic-unit approaches based on measured water quality factors such as trace metals are used to infer ecological impacts in the environment. However, it is uncertain whether the use of such approaches yields accurate risk predictions. To address this issue, we investigated and compared (1) water quality, including trace metals, and (2) benthic macroinvertebrate communities in a northern Japanese river receiving treated discharge from an abandoned mine and in a nearby reference river. As a sum-of-toxic-unit approach, we employed a cumulative criterion unit (CCU), namely, the sum of the ratios of the dissolved concentrations of a metal (Cu, Zn, Cd, or Pb) divided by the US Environmental Protection Agency hardness-adjusted environmental water quality criterion for that metal. Compared with the reference sites, at the metal-contaminated sites, the richness, abundance, and structure of macroinvertebrate communities were little affected, with CCUs of 1.7 to 7.4, suggesting that CCU values exceeding 1 do not always indicate marked adverse impacts on these metrics. Further study is still required to derive a more compelling conclusion on the generally applicable relationships between CCUs and ecological impacts on river invertebrates. This would lead to better ecological risk assessments based on sum-of-toxic-unit approaches.

Time to Bone Union after Hybrid Closed-Wedge High Tibial Osteotomy.

Medial open- and lateral closed-wedge high tibial osteotomy (hybrid CWHTO) can overcome the limitations of conventional CWHTO and open-wedge HTO (OWHTO) for medial compartmental osteoarthritis (OA) of the knee. Hybrid CWHTO increases stability by using a rigid locking plate and allows early full weight-bearing. However, the literature contains no information about time to bone union after this new procedure. The aim of this study is to evaluate the time to bone union after hybrid CWHTO. We reviewed 44 knees treated with hybrid CWHTO. Patients were able to stand on both legs on the day after surgery and walked with full weight-bearing within 4 weeks of the procedure. The time to achievement of bone union at the osteotomy site was defined as the number of months until bone union was confirmed on radiographic imaging. The mean time to radiographic confirmation of bone union was 4.5±1.5 months after surgery. Eleven knees (25.0%) required 6 months or more. Radiographic analysis and JOA score improved significantly between before and 1 year after surgery (p<0.01). Hybrid CWHTO is a very useful method for treating medial OA, but radiographic bone union requires 4.5 months on average. We must be aware of bone union after hybrid CWHTO.

Two Cases of High Tibial Osteotomy in Patients with Rheumatoid Arthritis Treated with Biologic Disease-modifying Anti-rheumatic Drugs.

High tibial osteotomy (HTO) procedure is generally contraindicated in rheumatoid arthritis (RA) patients because synovial inflammation may exacerbate joint damage post-surgery. The natural course of joint destruction in RA changed dramatically with new treatment strategies and the introduction of biologic disease-modifying anti-rheumatic drugs (bDMARDs). We report the cases of two RA patients who underwent HTO and whose disease activities were well controlled by bDMARDs. Despite their short follow-up periods, they showed acceptable objective and subjective clinical results. We believe that the combination of bDMARDs and HTO can be indicated for selected RA patients before total knee arthroplasty.

Quantifying Differences in Responses of Aquatic Insects to Trace Metal Exposure in Field Studies and Short-Term Stream Mesocosm Experiments.

Characterizing macroinvertebrate taxa as either sensitive or tolerant is of critical importance for investigating impacts of anthropogenic stressors in aquatic ecosystems and for inferring causality. However, our understanding of relative sensitivity of aquatic insects to metals in the field and under controlled conditions in the laboratory or mesocosm experiments is limited. In this study, we compared the response of 16 lotic macroinvertebrate families to metals in short-term (10-day) stream mesocosm experiments and in a spatially extensive field study of 154 Colorado streams. Comparisons of field and mesocosm-derived EC20 (effect concentration of 20%) values showed that aquatic insects were generally more sensitive to metals in the field. Although the ranked sensitivity to metals was similar for many families, we observed large differences between field and mesocosm responses for some groups (e.g., Baetidae and Heptageniidae). These differences most likely resulted from the inability of short-term experiments to account for factors such as dietary exposure to metals, rapid recolonization in the field, and effects of metals on sensitive life stages. Understanding mechanisms responsible for differences among field, mesocosm, and laboratory approaches would improve our ability to predict contaminant effects and establish ecologically meaningful water-quality criteria.

Does the Choice of NOEC or EC10 Affect the Hazardous Concentration for 5% of the Species?

We evaluated if the choice of no observed effect concentration (NOEC) or a 10% effect concentration (EC10) affects the hazardous concentrations for 5% of the species (HC5s) estimated from species sensitivity distributions (SSDs). By reviewing available literature reporting NOECs and reanalyzing original toxicity data to estimate EC10s, we developed two SSDs for five chemicals (zinc, lead, nonylphenol, 3,4-dichlorobenzenamine, and lindane) based separately on 9-19 EC10s and NOECs. On average, point estimates of HC5s based on EC10s were 1.2 (range of 0.6-1.9) times higher than those based on NOECs. However, both EC10-based and NOEC-based HC5s estimated for five substances were on the same order of magnitude, and their 95% confidence intervals overlapped considerably. Thus, although EC10 was chosen as a representative of ECx in this study, our results suggest that the choice of ECx (e.g., EC5, EC10, or EC20) or NOEC does not largely affect the resulting HC5s. Therefore, use of NOECs would be acceptable particularly in regulatory contexts, although the NOEC has important shortcomings and should be used with caution.

Predicting macroinvertebrate average score per taxon (ASPT) at water quality monitoring sites in Japanese rivers.

Biomonitoring with bioindicators such as river macroinvertebrates is fundamental for assessing the status of freshwater ecosystems. In Japan, water quality and biomonitoring surveys are conducted separately, leading to a lack of nationwide information on their relationships and the biological status of water quality monitoring (WQM) sites. To understand the biological status of WQM sites across Japan, we developed a multiple linear regression model to estimate the average score per taxon (ASPT) using river macroinvertebrate data surveyed at a total of 237 "aligned" sites based on the co-occurrence of biomonitoring and WQM sites. The resulting regression model with eight predictors, such as biological oxygen demand, the proportion of urban areas in the catchment, could predict ASPT with reasonable accuracy (e.g., an error of ±1 for 96% of the aligned data). Using this model, we estimated ASPT values at 2925 WQM sites in rivers nationwide, categorizing them into four levels of river environment quality: "very good" (29% of WQM sites), "good" (50%), "fairly good" (14%), and "not good" (8%). Furthermore, we observed statistically significant correlations (p < 0.05; 0.4 ≤ r ≤ 0.7) between ASPT and all eight macroinvertebrate metrics examined, such as mayfly and stonefly richness, providing ecological implications of changes in ASPT.

Triple jeopardy: The combined effects of viral, chemical, and thermal stress on kuruma prawn (Penaeus japonicus) juveniles.

Growing concerns have emerged over the combined effects of multiple stressors on ecosystems. Empirical evidence shows that the sensitivity of aquatic invertebrates to insecticides varies under thermally fluctuating conditions. Additionally, field surveys in estuarine areas of western Japan confirmed the presence of juvenile kuruma prawns (Penaeus japonicus) carrying the white spot syndrome virus (WSSV). Given the potential of co-exposure to multiple stressors, we performed a combined exposure experiment using a full-factorial design with three stressors: WSSV infection (presence or absence: initial 2 h exposure), fipronil (insecticide) exposure (0 or 0.1 µg/L: 14 d exposure), and temperature (20, 25, or 30 °C). We observed the highest mortality (75 %) in the WSSV + Fipronil treatment at 30 °C, with the associated specimens showing significant changes in the internal load of WSSV and concentrations of fipronil and its metabolite, fipronil sulfone. Severe perturbations of metabolites associated with increased energy expenditure and fatty acid utilization have been identified as potential factors underlying lethality in juvenile kuruma prawns. The results demonstrate that WSSV infection increases the susceptibility of thermally stressed juvenile kuruma prawns to fipronil. Therefore, further studies are required to determine the combined effects of multiple stressors in environmentally relevant scenarios on juvenile kuruma prawns as well as in estuarine ecosystems.

Modeling the effect of improved sewage disposal rates on ecological status for aquatic organisms in Japan.

Improving sewage disposal rates is an important policy for maintaining the health of aquatic organisms in river environments. In Japan, the rate is not yet 100 %. Two measures are necessary to eliminate the discharge of untreated greywater: (1) increase the number of households connected to sewage lines in areas with sewage systems, and (2) replace single-type household onsite wastewater treatment systems (OWTSs) with combined-type systems. To estimate the effect of improving the disposal rate on river water quality, we developed a hydrology-based organic pollution assessment model with a gridded spatial resolution of 250 m to estimate the biochemical oxygen demand (BOD) in rivers in Gunma Prefecture, Japan. We considered three scenarios based on the sewage disposal rate of 70.5 % in 2015. In Scenario A, the disposal rate is increased to 75.2 % in 2030 by increasing the connection rate to sewage lines. In Scenario B, the rate is increased to 88.2 % in 2030 through additional progress in converting from single-to combined-type OWTSs. In Scenario C, the rate reaches 100 % by 2040. The ecological status of rivers was evaluated using taxon richness of Ephemeroptera, Plecoptera, and Trichoptera estimated from its reported relationship to BOD. The number of sites in Gunma Prefecture polluted by organic waste classified as III (poor) and IV (very poor) was estimated to be 1610 under the present state (2015) and decreased to 1212 (25 % reduction) in Scenario A, 619 (62 % reduction) in Scenario B, and 50 (97 % reduction) in Scenario C, with the improvements mainly in small branch rivers. The effects of improved disposal rates were mainly evident in areas with relative high population densities using single-type OWTSs outside of areas with a sewage system, and measures taken in these areas were shown to be effective.

Can Chemical Toxicity in Saltwater Be Predicted from Toxicity in Freshwater? A Comprehensive Evaluation Using Species Sensitivity Distributions.

Species sensitivity distributions (SSDs) play an important role in ecological risk assessment. Estimating SSDs requires toxicity data for many species, but reports on saltwater species are often limited compared to freshwater species. This limitation can constrain informed management of saltwater quality for the protection of marine ecosystems. We investigated the relationships between the parameters (i.e., mean and standard deviation [SD]) of freshwater and saltwater log-normal SSDs to determine how accurately saltwater toxicity could be estimated from freshwater toxicity test data. We estimated freshwater and saltwater SSDs for 104 chemicals with reported acute toxicity data for five or more species and compared their means, SDs, and hazardous concentrations for 5% of the species (HC5) derived from the acute SSDs. Standard major axis regression analyses generally showed that log-log relationships between freshwater and saltwater SSD means, SDs, and HC5 values were nearly 1:1. In addition, the ratios of freshwater-to-saltwater SSD means and HC5 values for most of the 104 chemicals fell within the range 0.1-10. Although such a strong correlation was not observed for SSD SDs (r2 < 0.5), differences between freshwater and saltwater SSD SDs were relatively small. These results indicate that saltwater acute SSDs can be reasonably estimated using freshwater acute SSDs. Because the differences of the means and SDs between freshwater and saltwater SSDs were larger when the number of test species used for SSD estimation was lower (i.e., five to seven species in the present study), obtaining toxicity data for an adequate number of species will be key to better approximation of a saltwater acute SSD from a freshwater acute SSD for a given chemical. Environ Toxicol Chem 2022;41:2021-2027. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Comparison of Species Sensitivity Distributions for Sediment-Associated Nonionic Organic Chemicals Through Equilibrium Partitioning Theory and Spiked-Sediment Toxicity Tests with Invertebrates.

Equilibrium partitioning (EqP) theory and spiked-sediment toxicity tests are useful methods to develop sediment quality benchmarks. However, neither approach has been directly compared based on species sensitivity distributions (SSDs) to date. In the present study, we compared SSDs for 10 nonionic hydrophobic chemicals (e.g., pyrethroid insecticides, other insecticides, and polycyclic aromatic hydrocarbons) based on 10-14-day spiked-sediment toxicity test data with those based on EqP theory using acute water-only tests. Because the exposure periods were different between the two tests, effective concentrations (i.e., median effective/lethal concentration) were corrected to compare SSDs. Accordingly, we found that hazardous concentrations for 50% and 5% of species (HC50 and HC5, respectively) differed by up to a factor of 100 and 129 between the two approaches, respectively. However, when five or more species were used for SSD estimation, their differences were reduced to a factor of 1.7 and 5.1 for HC50 and HC5, respectively, and the 95% confidence intervals of HC50 values overlapped considerably between the two approaches. These results suggest that when the number of test species is adequate, SSDs based on EqP theory and spiked-sediment tests are comparable in sediment risk assessments. Environ Toxicol Chem 2022;41:462-473. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Stream Mesocosm Experiments Show no Protective Effects of Calcium on Copper Toxicity to Macroinvertebrates.

Although the concept and modeling of metal bioavailability and toxicity have been well developed based largely on laboratory experiments with standard test species, additional evidence is required to demonstrate their applicability for macroinvertebrates typically found in natural lotic ecosystems. We conducted 10-day stream mesocosm experiments to test the hypothesis that increased water hardness (in the present study, the calcium [Ca] concentration was increased by adding CaCl2 ) would mitigate the effects of copper (Cu) on natural benthic macroinvertebrate communities. Exposure of macroinvertebrate communities to 25 µg/L Cu for 10 days in stream mesocosm experiments resulted in significant decreases in total abundance, in number of taxa, and in abundance of many macroinvertebrate taxa. However, the addition of Ca to stream mesocosms and the associated increase in water hardness up to 250 mg/L CaCO3 did not mitigate these effects of Cu on macroinvertebrate communities. The results showed that the hardness-based water quality criteria for Cu of the US Environmental Protection Agency were not protective under the conditions of relatively high hardness, low alkalinity, and circumneutral pH. In contrast, the water quality criteria based on the biotic ligand model predicted little protective effects of Ca on Cu toxicity, which is consistent with our results. Additional experiments are required to understand the influence of modifying factors on the toxicity of metals to macroinvertebrate communities. Environ Toxicol Chem 2022;41:1304-1310. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Assessment of COVID-19 risk and prevention effectiveness among spectators of mass gathering events.

There is a need to evaluate and minimize the risk of novel coronavirus infections at mass gathering events, such as sports. In particular, to consider how to hold mass gathering events, it is important to clarify how the local infection prevalence, the number of spectators, the capacity proportion, and the implementation of preventions affect the infection risk. In this study, we used an environmental exposure model to analyze the relationship between infection risk and infection prevalence, the number of spectators, and the capacity proportion at mass gathering events in football and baseball games. In addition to assessing risk reduction through the implementation of various preventive measures, we assessed how face-mask-wearing proportion affects infection risk. Furthermore, the model was applied to estimate the number of infectors who entered the stadium and the number of newly infected individuals, and to compare them with actual reported cases. The model analysis revealed an 86-95% reduction in the infection risk due to the implementation of face-mask wearing and hand washing. Under conditions in which vaccine effectiveness was 20% and 80%, the risk reduction rates of infection among vaccinated spectators were 36% and 96%, respectively. Among the individual measures, face-mask wearing was particularly effective, and the infection risk increased as the face-mask-wearing proportion decreased. A linear relationship was observed between infection risk at mass gathering events and the infection prevalence. Furthermore, the number of newly infected individuals was also dependent on the number of spectators and the capacity proportion independent of the infection prevalence, confirming the importance of considering spectator capacity in infection risk management. These results highlight that it is beneficial for organisers to ensure prevention compliance and to mitigate or limit the number of spectators according to the prevalence of local infection. Both the estimated and reported numbers of newly infected individuals after the events were small, below 10 per 3-4 million spectators, despite a small gap between these numbers.