Profound regional disparities shaping the ecological risk in surface waters: A case study on cadmium across China

The scientific advancement of water quality criteria (WQC) stands as one of the paramount challenges in ensuring the security of aquatic ecosystem. The region-dependent species distribution and water quality characteristics would impact the toxicity of pollutant, which would further affect the derivation of WQC across regions. Presently, however, numerous countries adhere to singular WQC values. The "One-size-fits-all" WQC value for a given pollutant may lead to either "over-protection" or "under-protection" of organisms in specific region. In this study, we used cadmium(Cd) pollution in surface waters of China as a case study to shed light on this issue. This study evaluated critical water quality parameters and species distribution characteristics to modify WQC for Cd across distinct regions, thus unveiling the geographical variations in ecological risk for Cd throughout China. Notably, regional disparities in ecological risk emerged a substantial correlation with water hardness, while species-related distinctions magnified these regional variations. After considering the aforementioned factors, the variation in long-term WQC among different areas reached 84-fold, while the divergence in risk quotient extended to 280-fold. This study delineated zones of both heightened and diminished ecological susceptibility of Cd, thereby establishing a foundation for regionally differentiated management strategies.

Effects of water quality on palladium-induced olfactory toxicity and bioaccumulation in rainbow trout (Oncorhynchus mykiss)

Through emission processes, palladium (Pd) particulates from industrial sources are introduced into a range of ecosystems including freshwater environments. Despite this, research on Pd-induced bioaccumulation, uptake, and toxicity is limited for freshwater fishes. Unlike other metals, there are currently no regulations or protective guidelines to limit Pd release into aquatic systems, indicating a global absence of measures addressing its environmental impact. To assess the olfactory toxicity potential of Pd, the present study aimed to explore Pd accumulation in olfactory tissues, olfactory disruption, and oxidative stress in rainbow trout (Oncorhynchus mykiss) following waterborne Pd exposure. Olfactory sensitivity, measured by electro-olfactography, demonstrated that Pd inhibits multiple pathways of the olfactory system following 96 h of Pd exposure. In this study, the concentrations of Pd for inhibition of olfactory function by 20% (2.5 μg/L; IC20) and 50% (19 μg/L; IC50) were established. Rainbow trout were then exposed to IC20 and IC50 Pd concentrations in combination with varying exposure conditions, as changes in water quality alter the toxicity of metals. Independent to Pd, increased water hardness resulted in decreased olfactory perception owing to ion competition at the olfactory epithelium. No other environmental parameter in this study significantly influenced Pd-induced olfactory toxicity. Membrane-associated Pd was measured at the olfactory rosette and gill following exposure; however, this accumulation did not translate to oxidative stress as measured by the production of malondialdehyde. Our data suggest that Pd is toxic to rainbow trout via waterborne contamination near field-measured levels. This study further demonstrated Pd bioavailability and uptake at water-adjacent tissues, adding to our collective understanding of the toxicological profile of Pd. Taken together, our results provide novel insights into the olfactory toxicity in fish following Pd exposure. Integr Environ Assess Manag 2024;00:1-13. © 2024 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Water quality criteria and ecological risk assessment of lead (Pb) in China considering the total hardness of surface water: A national-scale study

Site-specific water quality criteria considering hydrochemical conditions are needed for zoning control of environmental risks. However, the differences in water quality parameters between regions have not been fully considered in the current research on water quality criteria and risk assessment of lead. In this study, lead concentration and total hardness (TH) data of surface water in 13 major river basins and 31 administrative regions in China were collected. Based on the normalization of the TH of the toxicity data, the short-term and long-term water quality criteria of lead in China's surface water in the specific TH condition (100 mg/L) were derived using the species sensitivity distribution method, which were 90.7 μg/L and 2.1 μg/L, respectively. Furthermore, this study provided general derivation formulas for the water quality criteria based on the TH of surface water and obtained the site-specific criteria for different regions/basins in China. On this basis, an ecological risk assessment considering the TH was proposed for the first time. The results showed that there was a clear risk of lead in the Pearl River Basin and the rivers in Zhejiang-Fujian. The southern coastal provinces were at an unacceptable risk level, although the lead concentrations in the surface water were medium; the opposite was true in northern China, which meant that a high concentration of lead did not necessarily pose a high ecological risk and about 25 % of the variation in the predicted risk can be explained by the TH in Monte Carlo simulation.

Do sediment-bound nickel and lead affect chironomids life-history? Toxicity assessment under environmentally relevant conditions

Metal pollution in aquatic ecosystems translates into increased concentrations of sediment-bound metals, representing a risk for benthic species. This risk might be enhanced in soft and moderately hard waters, world widely distributed, due to the protective role of hardness against metal toxicity. As lead (Pb) and nickel (Ni) are amongst the more abundant metals in aquatic systems, and since their combined effects to benthic species have been overlooked, in this study we aimed to investigate the life-cycle toxicity of Pb and Ni (using spiked sediment) to the benthic species Chironomus riparius, considering both single and mixture exposures, in moderately hard water. Environmentally relevant concentrations of each metal were used (25 and 75 mg kg^-1, based on a scenario of pollution by runoff waters from burnt forests), following a full factorial design. Effects of the mixture with the highest metal concentrations (Pb 75 mg kg^-1 dw + Ni 75 mg kg^-1 dw) were also assessed in the second generation. In the first generation, exposure to Pb increased emergence and the weight of males, and decreased time to emergence of both males and females. Conversely, exposure to Ni delayed female emergence and decreased the weight of imagoes. Summarizing, Pb affected more endpoints but showed an apparent positive effect, whereas Ni affected less endpoints but exhibited adverse effects. Reproduction was not affected by these metals. In the second generation, the mixture Pb 75 mg kg^-1 + Ni 75 mg kg^-1 dw delayed emergence and reduced the emerged female fraction and their weight. These results highlight that Pb and Ni can alter the structure of C. riparius populations at environmentally relevant concentrations, which signals potential repercussions in the dynamics and functioning of freshwater ecosystems under these contamination scenarios. The findings of the present study are relevant not only for metal-polluted environments, in general, but also for fire-affected ecosystems.

Overcoming barriers for nitrate electrochemical reduction: By-passing water hardness

Water matrix composition impacts water treatment performance. However, matrix composition impacts have rarely been studied for electrochemical water treatment processes, and the correlation between the composition and the treatment efficiency is lacking. This work evaluated the electrochemical reduction of nitrate (ERN) using different complex water matrices: groundwater, brackish water, and reverse osmosis (RO) concentrate/brine. The ERN was conducted using a tin (Sn) cathode because of the high selectivity towards nitrogen evolution reported for Sn electrocatalysts. The co-existence of calcium (Ca2+), magnesium (Mg2+), and carbonate (CO32-) ions in water caused a 4-fold decrease in the nitrate conversion into innocuous nitrogen gas due to inorganic scaling formation on the cathode surface. XRF and XRD analysis of fouled catalyst surfaces detected brucite (Mg(OH)2), calcite (CaCO3), and dolomite (CaMg(CO3)2) mineral scales formed on the cathode surface. Surface scaling created a physical barrier on the electrode that decreased the ERN efficiency. Identifying these main sources of ERN inhibition was key to devising potential fouling mitigation strategies. For this reason, the chemical softening pre-treatment of a real brackish water was conducted and this significantly increased nitrate conversion and faradaic efficiency during subsequent ERN treatment, leading to a lower electric energy consumption per order. Understanding the ionic foulant composition responsible for influencing electrochemically-driven technologies are the first steps that must be taken to move towards niche applications such as decentralized ERN. Thus, we propose either direct ERN implementation in regions facing high nitrate levels in soft waters, or a hybrid softening/nitrate removal system for those regions where high nitrate and high-water hardness appear simultaneously.

Exposure to Sri Lanka's local groundwater in a CKDu prevalent area causes kidney damage in zebrafish

How local groundwater induces chronic kidney disease of unknown etiology (CKDu) in Sri Lanka is still elusive. This study aims to elucidate the impacts of Sri Lanka's local groundwater in a CKDu prevalent area and reveal the possible pathogenic mechanism of CKDu using zebrafish models. The drinking water from the local underground well in Vavuniya was sampled and the water quality parameters including Na⁺, Mg²⁺, K⁺, Ca²⁺, Cl^-, NO^3-, SO₄^2-, and F^- were analyzed. Then, local groundwater exposure to zebrafish larvae and 293T cells was performed, and water with high hardness and fluoride was prepared as parallel groups. Our result showed that exposure to Sri Lanka's local groundwater caused developmental toxicity, kidney damage, and pronephric duct obstruction as well as abnormal behavior in zebrafish. Similar results were also found after exposure to water with high hardness and fluoride in zebrafish. Further, the expression levels of marker genes related to renal development and functions (foxj1a, dync2h1, pkd2, gata3, and slc20a1) were significantly altered, which is also confirmed in the 293T cells. Taken together, those results indicated that Sri Lanka's local groundwater in a CKDu prevalent area could cause kidney damage, implying that high water hardness and fluorine might be the inducible environmental factors for the etiological cause of CKDu.

Water hardness alleviates the stress response caused by waterborne zinc in goldfish Carassius auratus

In this study, the combined effect of waterborne Zn and water hardness on the stress response in the goldfish Carassius auratus was investigated. Goldfish were exposed to Zn concentrations of 0.5, 1.0, and 3.0 mg/L and water hardness of 90, 270, and 450 mg/L CaCO₃ for 1, 3, 7, and 14 d. After exposure, it was determined that higher the Zn concentration, the more obvious the stress response. However, the stress response reduced with increasing water hardness. An increase in the Zn concentration caused stress responses in fish according to the increase in the mRNA expressions of corticotropin-releasing hormone and adrenocorticotropic hormone and cortisol level in the hypothalamus-pituitary-interrenal axis. The expression of these factors was the highest on day 7 and decreased on day 14. Furthermore, to evaluate the stress change in the liver tissue, we analyzed alanine aminotransferase, aspartate aminotransferase, and heat shock protein 70 concentrations to determine the damage caused by Zn and the change in water hardness. Immunohistochemistry staining for Na⁺/K⁺-ATPase in the gills showed that the gill activity was inhibited by Zn, and an increase in water hardness could improve Na⁺/K⁺-ATPase. In conclusion, we found that increasing water hardness is a successful method to reduce the stress response in goldfish caused by Zn.

Derivation of site-specific guideline values for nitrate toxicity in Pilbara receiving waters with high hardness

The current study aimed to derive site-specific guideline values (SSGVs) for nitrate toxicity that are relevant to high hardness surface waters of the Pilbara region, north-western Australia, many of which receive nitrate-rich mine water discharges. The approach involved deriving SSGVs from a species sensitivity distribution (SSD) based on candidate data sets comprising toxicity data for local Pilbara species tested in local waters and nonlocal species tested under water quality conditions similar to those of local Pilbara waters. Water hardness was identified as the primary toxicity-modifying factor for nitrate that needed to be accounted for, with temperature and pH identified as supporting variables. Using ~10 years of local water quality data, primary and secondary criteria for hardness, temperature and pH were developed and used to select the most relevant toxicity data for the derivation. The selected toxicity data, which included data for four local species tested in local water and 10 nonlocal species tested under representative water quality conditions, were categorized according to the primary and secondary criteria. Using this categorization, four candidate nitrate toxicity data sets (n = 5, 10, 12, and 14) were assessed for their suitability to derive the SSGVs. The SSDs for all data sets yielded similar protective concentration (PC) values. Based on the best balance between the relevance of the toxicity data set to the local water quality conditions and the confidence in the PC values, the PC values based on data set 3 (12 species, six taxonomic groups) were identified as being the most appropriate for the SSGVs. The SSGVs for 99%, 95%, 90%, and 80% species protection were 7.6, 15, 23, and 39 mg/L NO₃ -N, respectively. An assessment of the appropriateness of the SSGVs indicated that they were likely to be appropriately protective of nitrate toxicity for the high hardness (i.e., ≥160 mg/L as CaCO₃ ) Pilbara receiving waters. Integr Environ Assess Manag 2022;18:1035-1046. © 2021 SETAC.

The influence of drinking water constituents on the level of microplastic release from plastic kettles

Microplastic (MP) release from household plastic products has become a global concern due to the high recorded levels of microplastic and the direct risk of human exposure. However, the most widely used MP measurement protocol, which involves the use of deionized (DI) water, fails to account for the ions and particles present in real drinking water. In this paper, the influence of typical ions (Ca²⁺/HCO₃^-, Fe³⁺, Cu²⁺) and particles (Fe₂O₃ particles) on MP release was systematically investigated by conducting a 100-day study using plastic kettles. Surprisingly, after 40 days, all ions resulted in a greater than 89.0% reduction in MP release while Fe₂O₃ particles showed no significant effect compared to the DI water control. The MP reduction efficiency ranking is Fe³⁺ ≈ Cu²⁺ > Ca²⁺/HCO₃^- > > Fe₂O₃ particles ≈ DI water. Physical and chemical characterization using SEM-EDX, AFM, XPS and Raman spectroscopy confirmed Ca²⁺/HCO₃^-, Cu²⁺ and Fe³⁺ ions are transformed into passivating films of CaCO₃, CuO, and Fe₂O₃, respectively, which are barriers to MP release. In contrast, there was no film formed when the plastic was exposed to Fe₂O₃ particles. Studies also confirmed that films with different chemical compositions form naturally in kettles during real life due to the different ions present in local regional water supplies. All films identified in this study can substantially reduce the levels of MP release while withstanding the repeated adverse conditions associated with daily use. This study underscores the potential for regional variations in human MP exposure due to the substantial impact water constituents have on the formation of passivating film formation and the subsequent release of MPs.

Significance of Mg-hardness and fluoride in drinking water on chronic kidney disease of unknown etiology in Monaragala, Sri Lanka

The epidemic of chronic kidney disease of unknown etiology (CKDu) that contributes significantly to morbidity and mortality rates among dry-zonal farming communities has become a public health priority in Sri Lanka. Though a large number of hypotheses were introduced as causative factors, none of them have been confirmed so far. As drinking water quality is among the most suspected causative factors for the emergence of CKDu, a detailed hydro-geochemical investigation was carried out concurrently with the population screening in the Monaragala district of Sri Lanka where high incidences of CKDu are reported. A population screening was performed selecting 46,754 people using both dipstick proteinuria test and Albumin-Creatinine Ratio (ACR). The results revealed that the disease prevalence is about 6.7 % in the district. A total of 60 groundwater samples, 30 each, were collected from CKDu-prevalent locations and control locations where there are no CKDu cases reported. The samples were analyzed to identify any possible linkage between water quality and disease prevalence. Concentrations of hardness, F^-, Na^+, and Mg²⁺ in groundwater revealed a statistically significant difference between CKDu and control wells at a confident level of p = 0.05. The study revealed that alkali (Na⁺+K⁺) and alkaline earth cations (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) were relatively higher in drinking water sources used by CKDu patients, compared to the well waters used by healthy individuals. Nearly 87 % of the wells used by CKDu cases showed higher fluoride levels that exceed the threshold level (1.0 mg L^-1). Contents of nephrotoxic trace elements such as As, Cd, and Pb were found to be comparable in both types of wells and were well below the WHO permissible levels, thus negating their prime influence on the CKDu prevalence. It is obtrusive that the elevated fluoride levels together with water hardness associated with higher Mg²⁺ levels have a possible relation with CKDu and may influence the disease progression.

Influence of various water quality parameters on passive sampler accumulation kinetics of different metal valencies in freshwater

Stabilized liquid membrane devices (SLMDs) have been used for passive integrative sampling of metals in freshwater systems. Field measurements of metal accumulation on SLMDs can provide a time-weighted average mass of labile metals over the deployment period. We exposed SLMDs in the laboratory to 0.5 μM solutions of silver, zinc, or aluminum as nitrate salts at three levels of water hardness, measuring metal accumulation every 4 days for 32 days. We saw linear accumulation in all experimental treatments, except for silver in high hardness (345.9 mg/L as CaCO₃). The time-accumulation relationships indicated that metal sorption rates vary across valency with the lower valency metals generally accumulating at greater rates. Water hardness also affected accumulation rates and accumulated mass with greater rates as hardness increased for zinc and aluminum. The accumulated zinc mass at 32 days in soft water was 78% of the mass in hard water for zinc, and accumulated aluminum mass was 29% of the mass in hard water. Factors such as oleate formation on the SLMD surface and solution chemistry, including pH and chemical speciation, were evaluated in explaining our results. Our work supports that SLMDs have utility for sampling metals in freshwater over extended time periods, which may be beneficial when there is limited access to sites; it also provide important interpretive guidance for the use of SLMDs.

Derivation of water quality criteria of zinc to protect aquatic life in Taihu Lake and the associated risk assessment

Zinc is a widely distributed environmental pollutants and has been listed as priority heavy metal pollutant in China. Similar as other heavy metals, toxicity of zinc to aquatic organisms affects by environmental factors such as water hardness. It is necessary to develop regional water quality criteria (WQC) to protect native aquatic life against zinc due to the diversity of aquatic organisms' variability across different water systems, as a concretization and supplement for national zinc WQC. This study derived WQC for zinc by species sensitivity distribution (SSD) curve method. The zinc toxicity data of the aquatic organisms in Taihu Lake used in SSD curve was collected based on published toxicity data for zinc with hardness values and supplemented with acute toxicity tests conducted in this study. Six aquatic organism natives to Taihu Lake were selected to conduct zinc acute toxicity test in a range of hardness conditions. The relationship between water hardness and zinc toxicity was constructed. The criterion maximum concentration (CMC) and criterion continuous concentration (CCC) for zinc in Taihu Lake were then derived, which considered the water quality and taxonomic groups in Taihu Lake. The CMC and CCC were 100.69 μg/L and 30.79 μg/L, respectively. The environmental risk of zinc to Taihu Lake are acceptable, at moderate to low levels. This study has provided a basis for regional water quality criterion derivation and risk assessment in China.

Development of regional water quality criteria of lead for protecting aquatic organism in Taihu Lake, China

Lead is a widely distributed priority controlled heavy metals in aquatic system, its toxicity to aquatic organisms affected by water quality parameters. This study investigated the acute toxicity of lead (Pb) to the aquatic organisms in Taihu Lake under various water hardness, corresponding regional water quality criteria were derived. The acute toxicity experimental results revealed that the toxicity of Pb to aquatic organisms increased with water hardness. The Pb toxicity has a highest toxicity at water hardness 50 mg/L (expressed as CaCO₃), especially for Palaemon modestus where the 96 h LC₅₀ value was 0.024 mg/L. The hazardous concentration for 5% of biological species (HC₅) values were determined via species sensitivity distribution (SSD) method as 94.0 μg/L, 222.3 μg/L and 375.8 μg/L for Pb at water hardness 50, 150, and 250 mg/L, respectively. The assessment factor (AF) value was set at 2, followed by the current SSD framework where European commission recommend a fixed AF of 5-1. Thus, the predicted no effect concentration (PNEC) values was 47.0 μg/L, 111.2 μg/Land 187.9 μg/L at water hardness 50, 150, and 250 mg/L, respectively. Meanwhile, the short-term water quality criteria of Pb for Taihu lake aquatic organisms were derived as 111.2 μg/L at water hardness 150 mg CaCO₃/L. The long-term water quality criteria were derived as 4.3 μg/L by using acute/chronic ratio 51.29. When the derived value was used for Taihu Lake, 2.7% of the sampling sites in Taihu Lake was exceeded this criterion. The results of this study can provide technical methods and basic information for deriving Pb regional water quality criteria for protecting native aquatic organisms, in China.

Adsorptive reduction of water hardness by a highly porous and regenerative geopolymer fabricated from coal fly ash waste with low-temperature calcination

In this research paper, potassium-activated geopolymer cubes (GeoC) fabricated from waste coal fly ash with low-temperature calcination were investigated as a water softening agent. The GeoC reduced water hardness contents by adsorbing calcium (Ca²⁺) and magnesium (Mg²⁺) ions from aqueous solutions. Batch experiments were conducted to investigate the adsorption performance for Ca²⁺ and Mg²⁺, including contact time, initial concentration of cations, and interference with competitive cations. The best performance for water hardness adsorption was found on GeoC-35, fabricated with the highest silicate ratio to hydroxide. The adsorption process reached equilibrium after a contact time of 6 h for Ca²⁺ and 24 h for Mg²⁺. The maximum adsorption capacity for Ca²⁺ and Mg²⁺ was 52.0 and 17.3 mg/g, respectively. Langmuir and pseudo-second-order models fitted the experimental data well, indicating that chemical reactions occurred on a homogeneous surface. The GeoC can also be reused for removing hardness. Furthermore, the increase in potassium and silicon concentration in solution varied directly with removal efficiency, suggesting that the aluminosilicate framework played a role in reducing water hardness via cationic exchange. The presence of competitive cations decreased adsorption ability, albeit it still exhibited an appreciable removal performance.

Coping strategies in response to different levels of elevated water hardness in channel catfish (Ictalurus punctatus): Insight into ion-regulatory and histopathological modulations

Water hardness above the optimal level can incite toxic effects in fish, which are often species specific. Hence, we aimed at obtaining insights on the potential effects of elevated water hardness as well as coping strategies in channel catfish (Ictalurus punctatus). First, a toxicity assay was performed where the 96 h-LC₅₀ was calculated as 4939 mg/L CaCO₃. Thereafter, to gain knowledge on the underlying adaptive strategies to high water hardness, fish were exposed to seven hardness levels (150, 600, 1000, 1500, 2000, 3000 and 4000 mg/L CaCO₃ at pH 8.15) for 15 days. Results showed that branchial activities of Ca²⁺-ATPase and Na⁺/K^+-ATPase, which facilitate Ca²⁺ uptake, reduced starting respectively from 1000 mg/L and 1500 mg/L CaCO₃. Nevertheless, Ca²⁺ burden in plasma and tissue (gills, liver and intestine) remained elevated. Hardness exposure also disturbed cations (Na⁺, K⁺, Mg²⁺) and minerals (iron and phosphorus) homeostasis in a tissue-specific and dose-dependent manner. Both hemoglobin content and hematocrit dropped significantly at 3000-4000 mg/L CaCO₃, with a parallel decline in iron content in plasma and gills. Muscle water content rose dramatically at 4000 mg/L CaCO₃, indicating an osmo-regulation disruption. Higher hardness of 3000-4000 mg/L CaCO₃ also incited a series of histopathological modifications in gills, liver and intestine; most likely due to excess Ca²⁺ accumulation. Overall, these data suggest that channel catfish can adapt to a wide range of elevated hardness by modulating Ca²⁺ regulatory pathways and histomorphological alterations, however, 1500 mg/L CaCO₃ and above can impair the performance of this species.

Progression of potential etiologies of the chronic kidney disease of unknown etiology in Sri Lanka

Chronic kidney disease of unknown etiology (CKDu) is a major health issue in agricultural areas in Sri Lanka. Despite many attempts to identifying causative factors of CKDu, the real cause/s remain/s elusive to date. Understanding the progression of potential etiologies may provide valuable insight into this quest. Literature relevant to CKDu addresses several etiologies, including quality of drinking water in the affected areas including hardness, fluoride, ionicity, agrochemical and heavy metal contaminations, consumption of contaminated food, and the genetic makeup of vulnerable populations. Progression of the etiologies revealed persistent interest in heavy metals of multiple origins: waterborne, foodborne, or soilborne. Secondary factors, such as water hardness, fluoride, and ionicity appear to act synergistically, aggravating the role of heavy metals on the onset, and the progression of CKDu. Demographical factors, such as male sex, over 50 years of age, agriculture-related occupation, and the consumption of contaminated water and food are intricately related with the disease progression while other minor risk factors such as smoking, alcohol consumption, etc. exasperate the disease condition. Since, none of these etiologies are examined adequately, conducting laboratory exposure studies under in-vivo and in-vitro settings to understand their role in CKDu is crucial.

Water hardness influenced variations in reproductive potential of two freshwater fish species; Poecilia reticulata and Betta splendens

OBJECTIVE

Hardness of water in the form of CaCO₃ affects reproductive potential in various fish species, differently. This study evaluates the effect of water hardness on growth and reproduction of two aquarium fishes, Poecilia reticulata (Ovo-viviparous sp.) and Betta splendens (Oviparous sp.) by growing them under 150 (control), 320, 540 and 900 ppm CaCO₃ levels in semi natural aquaria.

RESULTS

Growth increased with increasing water hardness, reporting a significant progress of P. reticulata (p = 0.005) at 900 ppm. Similarly, the reproductive potential of P. reticulata was improved significantly, recording the highest fecundity (16.22 ± 3.90) and Gonadosomatic Index (GSI-2.48 ± 0.6) at 900 ppm. However, in B. splendens water hardness adversely affected the reproduction by resulting a significantly low hatchability and disturbed bubble nests at 900 ppm, compared to the largest bubble nest formed at the control condition (108.58 ± 16.19 cm²). Thus, the study revealed differential effects of water hardness on reproductive potential of the test species, by increasing the potential of P. reticulata while decreasing that of B. splendens. Though larval survival was affected in both species, larval growth was improved significantly in P. reticulata at 900 ppm level. Understanding reproductive potential of aquarium fishes in natural waters is crucial for their management purposes.

Aquatic testing guidelines insufficiently control the influence of dilution water toc and hardness on cationic polymer toxicity - A proposal to improve standardized test procedures

Cationic polymers (CPs) are widely used chemicals for wastewater treatment applications and in various "down-the-drain" household products. The aquatic toxicity of CPs results from an electrostatic interaction with negatively charged cell surfaces. These effects are greatly mitigated by the binding affinity of CPs to total organic carbon (TOC) in surface water. Consequently, baseline aquatic toxicity tests of CPs using clean lab water (TOC < 2 mg/L) typically overestimate toxicity and risk which is greatly mitigated at higher environmentally relevant OC levels. However, the point at which mitigation begins is not well defined and low-level TOC in lab water may influence the baseline toxicity outcome. Similarly, divalent cations, quantified as water hardness, may modulate the electrostatic binding between OC and CP. Although standard guidelines define limits for lab water hardness and TOC, the consequences of variability within those limits on test outcome is unknown. We investigated the impact of part-per-billion (ppb) additions of TOC to lab water at different hardness levels on CP acute toxicity to Daphnia magna and Raphidocelis subcapitata. In both species, the acute toxicities of CPs with different molecular weight and charge density varied by > 10-fold in response to slight changes in TOC and water hardness, although parameters were maintained within guideline limits. When determining the baseline aquatic toxicity of CPs, the lab water should be standardized at the lowest biologically tolerable hardness and TOC at a reliably measurable level (>1 - < 2 mg/L) to reduce variability and increase the reliability of the toxicity estimate.

The Role of Environmental Exposures in Atopic Dermatitis

PURPOSE OF REVIEW

Although genetic factors clearly play a role in the development of atopic dermatitis (AD), the recent dramatic increase in the prevalence of AD in low- and middle-income countries is not consistent with only a role of genetic factors. These findings strongly suggest that environmental factors may play an important role in the pathogenesis of AD.

RECENT FINDINGS

We reviewed the role of gene-environment studies; in utero exposures including tobacco smoke, alcohol, maternal stress, various digestive supplements, and gestational diabetes; early-life exposures including diet, gut microbiota, antibiotics, and breastfeeding; climate including temperature, ultraviolet radiation exposure, and air pollution; and household products, indoor allergens, water hardness, pH, and skin microbiota and their effects on AD. Environmental factors definitely play a role in the pathogenesis of AD. However, identifying definitive factors continues to be difficult in the setting of conflicting evidence and the complex interactions between genotypes and the environment resulting in a multitude of AD phenotypes. All of the different environmental interactions discussed highlight the importance of intervening on multiple levels in a patient's environment to improve or even prevent AD symptoms. Further, the importance of modifying environmental factors early on in a person's life is demonstrated. When possible, all of these environmental factors should be considered in treating a patient with AD and the appropriate modifications should be made at population and individual levels.

Experimental rat model for acute tubular injury induced by high water hardness and high water fluoride: efficacy of primary preventive intervention by distilled water administration

Background

High water hardness associated with high water fluoride and the geographical distribution of Chronic Kidney Disease of unknown etiology (CKDu) in Sri Lanka are well correlated. We undertook this study to observe the effects of high water hardness with high fluoride on kidney and liver in rats and efficacy of distilled water in reducing the effects.

Methods

Test water sample with high water hardness and high fluoride was collected from Mihinthale region and normal water samples were collected from Kandy region. Twenty-four rats were randomly divided into 8 groups and water samples were introduced as follows as daily water supply. Four groups received normal water for 60 (N1) and 90 (N2) days and test water for 60 (T1) and 90 (T2) days. Other four groups received normal (N3) and test (T3) water for 60 days and followed by distilled water for additional 60 days and normal (N4) and test (T4) water for 90 days followed by distilled water for another 90 days. The rats were sacrificed following treatment. Serum samples were subjected to biochemical tests; serum creatinine, urea, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP) and elemental analysis. Histopathological examinations were carried out using kidney and liver samples.

Results

Test water treated groups were associated with acute tubular injury with loss of brush border and test water followed with distilled water treated groups maintained a better morphology with minimal loss of brush border. Serum creatinine levels in T1 and T2 groups and urea level in T2 group were significantly (p < 0.05) increased compared to control groups. After administration of distilled water, both parameters were significantly reduced in T4 group (p < 0.05) compared to T2. Serum AST activity was increased in T4 group (p < 0.05) compared to control group with no histopathological changes in liver tissues. The serum sodium levels were found to be much higher compared to the other electrolytes in test groups.

Conclusion

Hard water with high fluoride content resulted in acute tubular injury with a significant increase in serum levels of creatinine, urea and AST activity. These alterations were minimized by administering distilled water.

Transcriptome analysis of the fish pathogen Flavobacterium columnare in biofilm suggests calcium role in pathogenesis

BACKGROUND

Flavobacterium columnare is the causative agent of columnaris disease that affects cultured freshwater fishes worldwide. F. columnare easily colonizes surfaces by forming biofilm, which helps the pathogen resist antibiotic and disinfectant treatments. Previously, we had shown that increasing concentrations of calcium (Ca²⁺) promoted biofilm formation by F. columnare. The objective of this study was to further characterize the role of Ca²⁺ on biofilm formation and to compare the transcriptome profiles of planktonic and biofilm cells.

RESULTS

RNA-Seq analysis was conducted to identify genes that were differentially expressed between the following states: i) planktonic cells in control medium (P), ii) planktonic cells in calcium-enriched medium (P/Ca), and iii) biofilm cells in calcium-enriched medium (B/Ca). Overall, we identified 441 significant (FDR-adjusted p < 0.05, fold change > 2) differentially expressed genes (DEGs) between P and B/Ca samples; 112 significant DEGs between P/Ca and B/Ca samples, and 175 significant DEGs between P/Ca and P samples, corresponding to 15.87, 4.03 and 6.30% of the total protein-coding sequences, respectively. The significant DEGs fell into different functional categories including iron acquisition, oxidative stress response, extracellular protein secretion, and respiratory metabolism.

CONCLUSIONS

Our results posit Ca²⁺ as a critical signal in regulating bacterial surface adhesion and biofilm formation in F. columnare. Living in biofilm elicited a shift in several metabolic pathways that allowed the cells to cope with oxidative stress and nutrient starvation. In addition, Ca²⁺ supplementation induced the expression of putative virulence factors in F. columnare, such as extracellular protein secretion and iron acquisition.

Association of consumption of excess hard water, body mass index and waist circumference with risk of hypertension in individuals living in hard and soft water areas

Chronic exposure to soft drinking water increases the risk of hypertension. We conducted a cross-sectional study in 2017 in two study areas in the Poldasht County to assess the relation of hardness, body mass index and waist circumference with risk of hypertension. Total water hardness was measured by gravimetric methods. Hardness of > 180 ppm was considered to be hard drinking water. The Shiblu and Gharghologh areas had a four times higher mean total hardness level in drinking water (968.69 mg/L as CaCO₃) than the Sarisoo and Agh Otlogh (180 mg/L as CaCO₃) areas. According to the results of the study, the prehypertension prevalence in areas with high and low water hardness was calculated as 23.15% (18.11-29.15) and 46.84% (37.61-57.64), respectively. Moreover, the result showed the prevalence of hypertension and prehypertension was higher in regions with low hardness than those with high hardness, which was statistically significant (P < 0.001). The results of logistic regression showed that age, body mass index, waist circumference and hardness of drinking water were significantly related to hypertension. Accordingly, hypertension was low in people of regions with high hardness (OR 0.26, 0.17-0.42). This report examined whether total hardness in drinking water was protective against hypertension. This is an important finding for the ministry of human health as well as for the water and sewage company.

Effect of water source and feed regime on development and phenotypic quality in Anopheles gambiae (s.l.): prospects for improved mass-rearing techniques towards release programmes

Background

In many malaria-endemic sub-Saharan countries, insecticide resistance poses a threat to existing mosquito control measures, underscoring the need for complementary control methods such as sterile and/or genetically-modified mosquito release programmes. The sibling species Anopheles gambiae and An. coluzzii are responsible for malaria transmission in most of this region. In their natural habitat, these species generally breed in clean, soft water and it is believed that divergent preference in their larval breeding sites have played a role in their speciation process. Mosquito release programmes rely on the rearing of mosquitoes at high larval densities. Current rearing protocols often make use of deionised water regardless of the strain reared. They also depend on a delicate balance between the need for adequate feeding and the negative effect of toxic ammonia and food waste build-up on mosquito development, making managing and improving water quality in the insectary imperative.

Methods

Here, we investigated the impact of water source and feed regimes on emergence rate and phenotypic quality of mosquitoes in the insectary. First-instar larvae of An. gambiae (Kisumu strain) and An. coluzzii (Mopti and VK3 strains) were reared in three water sources with varying degrees of hardness (deionised, mineral and a mix of the two), with a daily water change. Larvae were fed daily using two standardised feeding regimes, solution and powder feed.

Results

Water source had a significant impact on mosquito size and development time for all strains. Earlier emergence of significantly larger mosquitoes was observed in mineral water with the smallest mosquitoes developing later from deionised water. Wing-length was significantly longer in mineral, mixed water and in powder feed, irrespective of sex, strains or water types. Deionised water was the least favourable for mosquito quality across all strains.

Conclusions

Mineral water and powder feed should be used in rearing protocols to improve mosquito quality where the optimal quality of mosquitoes is desired. Although results obtained were not significant for improved mosquito numbers, the phenotypic quality of mosquitoes reared was significantly improved in mineral water and mix water. Further studies are recommended on the impact mineral water has on other fitness traits such as longevity, fecundity and mating competitiveness.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3465-0) contains supplementary material, which is available to authorized users.

Physical characteristics of ceramic/glass-polymer based CAD/CAM materials: Effect of finishing and polishing techniques

PURPOSE

The aim of this study was to compare the effect of different finishing and polishing techniques on water absorption, water solubility, and microhardness of ceramic or glass-polymer based computer-aided design and computer-aided manufacturing (CAD/CAM) materials following thermocycling.

MATERIALS AND METHODS

150 disc-shaped specimens were prepared from three different hybrid materials and divided into five subgroups according to the applied surface polishing techniques. All specimens were subjected up to #4000 grit SiC paper grinding. No additional polishing has been done to the control group (Group I). Other polishing procedures were as follows: Group II: two-stage diamond impregnated polishing discs; Group III: yellow colored rubber based silicone discs; Group IV: diamond polishing paste; and Group V: Aluminum oxide polishing discs. Subsequently, 5000-cycles of thermocycling were applied. The analyses were conducted after 24 hours, 7 days, and 30 days of water immersion. Water absorption and water solubility results were analyzed by two-way ANOVA and Tukey post-hoc tests. Besides, microhardness data were compared by Kruskal-Wallis and Mann-Whitney U tests (P<.05).

RESULTS

Surface polishing procedures had significant effects on water absorption and solubility and surface microhardness of resin ceramics (P<.05). Group IV exhibited the lowest water absorption and the highest microhardness values (P<.05). Immersion periods had no effect on the microhardness of hybrid ceramic materials (P>.05).

CONCLUSION

Surface finishing and polishing procedures might negatively affect physical properties of hybrid ceramic materials. Nevertheless, immersion periods do not affect the microhardness of the materials. Final polishing by using diamond polishing paste can be recommended for all CAD/CAM materials.

Grafting polymerization of acrylic acid onto chitosan-cellulose hybrid and application of the graft as highly efficient ligand for elimination of water hardness: Validation of high selectivity in presence of interfering ions

Graft Copolymer resulting from polymerization of acrylic acid from chitosan is non-coherent, brittle and exhibit modest swelling in water, which limits its application. Chitosan-cellulose hybrid was initially prepared and novel polymeric ligand ((CTS/Cell)-g-PAA) derived from grafting polymerization of acrylic acid from this hybrid was fabricated and investigated using fourier transform infrared (FTIR) and Scanning electron microscopy (SEM). Also, the graft copolymer exhibited high mass transfer under a wide range of pH values due to its elevated hydrophilicity in addition to a good mechanical strength with respect to the comparable graft derived from chitosan as sole backbone for the grafting. The high content of different oxygen and nitrogen-containing groups in a crowded chemical atmosphere along with the high swelling qualified the graft to act as very efficient polymeric ligand with high capacity of removal of metal ions from water under broad conditions. The polymeric ligand performed outstandingly and competitively in the removal of water hardness even in presence of other interfering ions.

Tracing environmental aetiological factors of chronic kidney diseases in the dry zone of Sri Lanka-A hydrogeochemical and isotope approach

Chronic kidney disease of unknown aetiologies (CKDu) is increasingly recognized in tropical regions and is now considered a global health problem. A detailed hydrogeochemical investigation has been performed in three CKDu hotspots in Sri Lanka to assess the geo-environmental aetiological factors influencing this disease. A total of 71 ground- and 26 surface water samples were collected from Girandurukotte, Wilgamuwa and Nikawewa regions and analysed for major constituents and trace elements. The affected regions are dominated by Ca-Mg-HCO₃ facies groundwater that is mainly controlled by silicate weathering. Higher levels of fluoride associated with higher hardness is the main feature of groundwater from CKDu regions compared to non-CKDu regions. Results showed that 65% of the wells in the affected regions exceeded the fluoride concentration of 0.5mg/L. Environmental isotopes of groundwater in the CKDu regions are represented by the regression line of δ²H=5.42δ¹⁸O-3.59 (r²=0.916) with a clear isotopic differentiation between local precipitation and groundwater. None of the trace elements exceeded the recommended scales and in most cases levels are negligible in both surface and groundwater in study areas. Therefore, the involvement of trace elements such as Cd, As and Pb can be ignored as causative factors for CKDu. This study highlights the synergistic influence of fluoride and hardness that could enhance the disease, and thereby refute earlier theories that attribute trace elements as causative factors for CKDu. Higher hardness in drinking water also restricts sufficient water uptake, particularly by farmers and which affects the physiological, biochemical and nutritional requirements.

Microbial mediated desalination for ground water softening with simultaneous power generation

A novel three-chambered microbial desalination cell (MDC) was designed for evaluating desalination of synthetic ground water with simultaneous energy generation and resource recovery. The specific design enabled efficient interelectrode communication by reducing the distance of separation and also maintained an appropriate surface area to volume ratio. MDC were evaluated in different circuitry modes (open and closed) to assess the desalination efficiency, bioelectricity generation, resource recovery, substrate utilization and bioelectrokinetics. The closed circuit operation has showed efficient desalination efficiency (51.5%) and substrate utilization (70%). Owing to the effective electron transfer kinetics, closed circuit mode of operation showed effective desalination of the synthetic ground water with simultaneous power production (0.35W/m²). Circuitry specific biocatalyst activity was observed with higher peak currents (10.1mA; -5.98mA) in closed circuit mode. MDC can function as sustainable and alternative solution for ground and surface water treatment with power productivity and resource recovery.

Effect of Water Hardness on Efficacy of Sodium Hypochlorite Inactivation of Escherichia coli O157:H7 in Water

This study examined how the hardness of water affected the efficacy of sodium hypochlorite in inactivating Escherichia coli O157:H7 in water. Water was prepared at different degrees of total hardness (0, 50, 100, 200, 500, 1,000, 2,000, and 5,000 mg/liter CaCO₃). Inactivation was assessed at different levels of free chlorine (0, 0.2, 0.5, and 1.0 ppm) at 2 to 4°C and pH 6.5. Thirty milliliters of chlorinated water was inoculated with 6 log CFU/ml of E. coli O157:H7 and allowed to mix for 3, 10, 20, or 30 s. In the absence of sodium hypochlorite, no reduction in counts of E. coli O157:H7 was observed regardless of the degree of water hardness. However, in the presence of hard water, under certain chlorine concentrations and exposure times, the reduction of E. coli O157:H7 in chlorinated hard water was significantly less than the reduction observed in chlorinated deionized water. For example, after exposure to 0.5 ppm of free chlorine for 10 s, E. coli O157:H7 counts were reduced by 4.8 ± 1.4, 2.0 ± 1.3, 1.6 ± 0.7, 0.5 ± 0.7, and 0.0 ± 0.1 log CFU/ml in water containing 0, 100, 1,000, 2,000, and 5,000 mg/liter CaCO₃, respectively. With the exception of 5,000 mg/liter CaCO₃, the effect of water hardness was no longer visible after 20 s of exposure to 0.5 ppm of free chlorine. Also, hard water significantly lowered the efficacy of sodium hypochlorite at 3 s of exposure to 1.0 ppm of free chlorine. But after 20 s of exposure to 1.0 ppm of free chlorine, the impact of water hardness was no longer observed. This study demonstrated that water hardness can affect the germicidal efficacy of sodium hypochlorite, and such an impact may or may not be apparent depending on the condition of the solution and the treatment time at which the observation is made. Under the conditions typically seen in commercial produce washing operations, the impact of water hardness on chlorine efficacy is likely to be insignificant compared with that of organic load.

Natural fluoride in drinking water and myocardial infarction: A cohort study in Sweden

Large geographical variation in the coronary heart disease (CHD) incidence is seen worldwide and only a part of this difference is attributed to the classic risk factors. Several environmental factors, such as trace elements in the drinking water have been implicated in the pathogenesis of CHD. The objective was to assess the association between drinking water fluoride exposure and myocardial infarction in Sweden using nationwide registers. This large cohort consisted of 455,619 individuals, born in Sweden between January 1, 1900 and December 31, 1919, alive and living in their municipality of birth at the time of start of follow-up. Estimated individual drinking water fluoride exposure was stratified into four categories: very low (<0.3mg/l), low (0.3-<0.7mg/l), medium (0.7-<1.5mg/l) and high (≥1.5mg/l). In Cox regression analyses, compared to the very low fluoride group, the adjusted Hazard Ratio for the low fluoride group was 0.99 (95% confidence interval, 0.98-1.00), for the medium fluoride group 1.01 (95% confidence interval, 0.99-1.03) and 0.98 (95% confidence interval, 0.96-1.01) for the highest fluoride group. Adding water hardness to the model did not change the results. We conclude that the investigated levels of natural drinking water fluoride content does not appear to be associated with myocardial infarction, nor related to the geographic myocardial infarction risk variation in Sweden. Potential misclassification of exposure and unmeasured confounding may have influenced the results.

Revisiting the mechanisms of copper toxicity to rainbow trout: Time course, influence of calcium, unidirectional Na(+) fluxes, and branchial Na(+), K(+) ATPase and V-type H(+) ATPase activities

In order to resolve uncertainties as to the mechanisms of toxic action of Cu and the protective effects of water [Ca], juvenile rainbow trout were acclimated to baseline soft water (SW, [Na(+)]=0.07, [Ca(2+)]=0.15, [Mg(2+)]=0.05mmolL(-1)) and then exposed to Cu with or without elevated [Ca] but at constant titratable alkalinity (0.27mmolL(-1)). The 96-h LC50 was 7-fold higher (63.8 versus 9.2μgCuL(-1); 1.00 versus 0.14μmolCuL(-1)) at [Ca]=3.0 versus 0.15mmolL(-1). Gill Cu burden increased with exposure concentration, and higher [Ca] attenuated this accumulation. At 24h, the gill Cu load (LA50≈0.58μgCug(-1); 9.13nmolCug(-1)) predictive of 50% mortality by 96h was independent of [Ca], in accord with Biotic Ligand Model (BLM) theory. Cu exposure induced net Na(+) losses (J(Na)net) by increasing unidirectional Na(+) efflux rates (J(Na)out) and inhibiting unidirectional Na(+) uptake rates (J(Na)in). The effect on J(Na)out was virtually immediate, whereas the effect on J(Na)in developed progressively over 24h and was associated with an inhibition of branchial Na(+), K(+) ATPase activity. The J(Na)in inhibition was eventually significant at a lower Cu threshold concentration (15μgCuL(-1)) than the J(Na)out stimulation (100μg Cu L(-1)). Elevated Ca protected against both effects, as well as against the inhibition of Na(+), K(+) ATPase activity. Branchial V-type H(+) ATPase activity was also inhibited by Cu exposure (100μgCuL(-1)), but only after 24h at high [Ca] (3.0mmolL(-1)). These novel results therefore reinforce the applicability of BLM theory to Cu, clarify that whether Na(+) influx or efflux is more sensitive depends on the duration of Cu exposure, show that elevated water [Ca], independent of alkalinity, is protective against both mechanisms of Cu toxicity, and identify V-type H(+)ATPase as a new Cu target for future investigation.

Rapid changes in water hardness and alkalinity: Calcite formation is lethal to Daphnia magna

There is growing concern that freshwater ecosystems may be negatively affected by ever-increasing anthropogenic inputs of extremely hard, highly alkaline effluent containing large quantities of Ca(2+), Mg(2+), CO3(2-), and HCO3(-) ions. In this study, the toxicity of rapid and extreme shifts in water hardness (38-600mg/L as CaCO3) and alkalinity (30-420mg/L as CaCO3) to Daphnia magna was tested, both independently and in combination. Within these ranges, where no precipitation event occurred, shifts in water hardness and/or alkalinity were not toxic to D. magna. In contrast, 98-100% of D. magna died within 96h after exposure to 600mg/L as CaCO3 water hardness and 420mg/L as CaCO3 alkalinity (LT50 of 60h with a 95% CI of 54.2-66.0h). In this treatment, a CaCO3 (calcite) precipitate formed in the water column which was ingested by and thoroughly coated the D. magna. Calcite collected from a mining impacted stream contained embedded organisms, suggesting field streams may also experience similar conditions and possibly increased mortality as observed in the lab tests. Although further investigation is required to determine the exact fate of aquatic organisms exposed to rapid calcite precipitation in the field, we caution that negative effects may occur more quickly or at lower concentrations of water hardness and alkalinity in which we observed effects in D. magna, because some species, such as aquatic insects, are more sensitive than cladocerans to changes in ionic strength. Our results provide evidence that both calcite precipitation and the major ion balance of waters should be managed in industrially affected ecosystems and we support the development of a hardness+alkalinity guideline for the protection of aquatic life.

The Effect of Water Hardness on Mortality of Zebrafish (Danio rerio) During Exposure to Oxytetracycline

Marking of fish otoliths with oxytetracycline and tetracycline is a widely used method to evaluate the effectiveness of stocking operations. Available protocols for the labeling of fish specify a number of factors influencing mark quality and potential risk for fish during marking. This study investigates the influence of water hardness on mortality of freshwater fish during marking with OTC. In order to pursue this question complexation of OTC with Mg(2+) and Ca(2+) cations was measured spectrophotometrically. Furthermore, zebrafish (Danio rerio) were immersed in OTC solutions (1200 mg/L; 48 h immersion) combined with varying levels of water hardness (5.5, 15.5, 25.5, 32.5°dH). The amount of OTC-Mg-Ca-complexes was positively correlated to water hardness. Moreover, it could be demonstrated that mortality of zebrafish during marking varied as a factor of water hardness. Highest mortalities occurred at the lowest (5.5°dH) and the highest (32.5°dH) tested levels during marking with OTC.

Toxicity of lead (Pb) to freshwater green algae: development and validation of a bioavailability model and inter-species sensitivity comparison

Scientifically sound risk assessment and derivation of environmental quality standards for lead (Pb) in the freshwater environment are hampered by insufficient data on chronic toxicity and bioavailability to unicellular green algae. Here, we first performed comparative chronic (72-h) toxicity tests with three algal species in medium at pH 6, containing 4 mg fulvic acid (FA)/L and containing organic phosphorous (P), i.e. glycerol-2-phosphate, instead of PO4(3-) to prevent lead-phosphate mineral precipitation. Pseudokirchneriella subcapitata was 4-fold more sensitive to Pb than Chlorella kesslerii, with Chlamydomonas reinhardtii in the middle. The influence of medium physico-chemistry was therefore investigated in detail with P. subcapitata. In synthetic test media, higher concentrations of fulvic acid or lower pH protected against toxicity of (filtered) Pb to P. subcapitata, while effects of increased Ca or Mg on Pb toxicity were less clear. When toxicity was expressed on a free Pb(2+) ion activity basis, a log-linear, 260-fold increase of toxicity was observed between pH 6.0 and 7.6. Effects of fulvic acid were calculated to be much more limited (1.9-fold) and were probably even non-existent (depending on the affinity constant for Pb binding to fulvic acid that was used for calculating speciation). A relatively simple bioavailability model, consisting of a log-linear pH effect on Pb(2+) ion toxicity linked to the geochemical speciation model Visual Minteq (with the default NICA-Donnan description of metal and proton binding to fulvic acid), provided relatively accurate toxicity predictions. While toxicity of (filtered) Pb varied 13.7-fold across 14 different test media (including four Pb-spiked natural waters) with widely varying physico-chemistry (72h-EC50s between 26.6 and 364 μg/L), this bioavailability model displayed mean and maximum prediction errors of only 1.4 and 2.2-fold, respectively, thus indicating the potential usefulness of this bioavailability model to reduce uncertainty in site-specific risk assessment. A model-based comparison with other species indicated that the sensitivity difference between P. subcapitata and two of the most chronically Pb-sensitive aquatic invertebrates (the crustacean Ceriodaphnia dubia and the snail Lymnaea stagnalis) is strongly pH dependent, with P. subcapitata becoming the most sensitive of the three at pH > 7.4. This indicates that inter-species differences in Pb bioavailability relationships should be accounted for in risk assessment and in the derivation of water quality criteria or environmental quality standards for Pb. The chronic toxicity data with three algae species and the bioavailability model presented here will help to provide a stronger scientific basis for evaluating ecological effects of Pb in the freshwater environment.

Financial and environmental modelling of water hardness--implications for utilising harvested rainwater in washing machines

A study was conducted to determine the financial and environmental effects of water quality on rainwater harvesting systems. The potential for replacing tap water used in washing machines with rainwater was studied, and then analysis presented in this paper is valid for applications that include washing machines where tap water hardness may be important. A wide range of weather conditions, such as rainfall (284-1,794 mm/year); water hardness (14-315 mg/L CaCO3); tap water prices (0.85-2.65 Euros/m(3)) in different Spanish urban areas (from individual buildings to whole neighbourhoods); and other scenarios (including materials and water storage capacity) were analysed. Rainfall was essential for rainwater harvesting, but the tap water prices and the water hardness were the main factors for consideration in the financial and the environmental analyses, respectively. The local tap water hardness and prices can cause greater financial and environmental impacts than the type of material used for the water storage tank or the volume of the tank. The use of rainwater as a substitute for hard water in washing machines favours financial analysis. Although tap water hardness significantly affects the financial analysis, the greatest effect was found in the environmental analysis. When hard tap water needed to be replaced, it was found that a water price of 1 Euro/m(3) could render the use of rainwater financially feasible when using large-scale rainwater harvesting systems. When the water hardness was greater than 300 mg/L CaCO3, a financial analysis revealed that an net present value greater than 270 Euros/dwelling could be obtained at the neighbourhood scale, and there could be a reduction in the Global Warming Potential (100 years) ranging between 35 and 101 kg CO2 eq./dwelling/year.