Elevated concentrations of sulfate in waterways are observed due to various anthropogenic activities. Elevated levels of sulfate can have harmful effects on aquatic life in freshwaters: sulfate can cause osmotic stress or specific ion toxicity in aquatic organisms, especially in soft waters where Ca²⁺ and Mg²⁺ concentrations are low. Formerly, chronic toxicity test data in soft water have been scarce. The chronic and acute sulfate toxicity tests conducted with aquatic organisms from 10 families across various trophic levels in this study multiplied the number of tests conducted in soft freshwater conditions and enabled derivation of the species sensitivity distribution (SSD) and sulfate hazardous concentrations for soft freshwaters. The cladoceran Daphnia longispina and freshwater snail Lymnaea stagnalis were the most sensitive to sulfate among the studied species. Harmful effects on the reproduction of D. longispina were observed at 49 mg SO₄ /L while growth of L. stagnalis was inhibited at 217 mg SO₄ /L. Most studied organisms tolerated high sulfate concentrations: the median of chronic effective concentrations (EC10 or LC10) was 1008 mg/L for all the species tested in this study. Based on the species sensitivity distribution of the studied species the hazardous concentration for 5 % of aquatic organism (HC5) in soft waters was 117-194 mg SO₄/L. Different data set combinations were used to demonstrate the data variability in SSD-based HC5 estimates. The lowest values were produced from combining biotest results from the present study and earlier literature, while the highest values were calculated from the present study only. The derived chronic no-effect concentrations (PNEC) varied between 39 and 65 mg SO₄/L.

Sulfate is found naturally in the aquatic environments, but due to various anthropogenic activities the sulfate concentrations in surface waters have increased globally. High levels of sulfate can cause adverse effects on aquatic organisms. In this study we explored the effects of sulfate on the reproduction of two coregonine species, whitefish (Coregonus lavaretus (L.)) and vendace (Coregonus albula (L.)), in Baltic Sea brackish water and soft boreal freshwater. The chronic toxicity tests lasted from fertilization to hatching of the larvae, endpoints being embryonic and larval survival, and size of newly hatched larvae. The chronic 196–214-day tests were conducted in different sodium sulfate (Na₂SO₄) solutions at water temperatures simulating natural conditions during the egg incubation from autumn to spring. The separate fertilization tests were carried out to measure fertilization success (%). The fertilization and early embryonic phase were found to be the most sensitive periods for sulfate toxicity. The survival in late embryonic phase, hatching and 5-day larval phase was high (>80%). In the acute fertilization tests with brackish water populations, the LC50-values were between 2554 and 2575 mg/L and with freshwater populations between 1107 and 1230 mg/L of sulfate. In the chronic experiments from fertilization to hatching the LC10-values for brackish water populations were between 1800 and 1820 mg/L and for freshwater populations between 335 and 624 mg/L of sulfate. The tolerance for sulfate in freshwater coregonines was significantly lower than brackish water coregonines, but it was in similar range as to what has been observed in other freshwater species.

Sulfate is increasingly found in elevated concentrations in freshwater ecosystems due to anthropogenic activities. Chronic exposure to sulfate has been reported to cause sublethal effects on freshwater invertebrates. Previous sulfate toxicity tests have mostly been conducted in hard or moderately hard waters, and research on species inhabiting soft water is needed, given that freshwater organisms face heightened sensitivity to toxicants in water of lower hardness. In the present study, we examined sulfate sensitivity of two endangered freshwater mussel species, Unio crassus, and Margaritifera margaritifera. Glochidia and juveniles of both species were subjected to acute and/or chronic sulfate exposures in soft water to compare sulfate sensitivity across age groups, and effective concentrations (EC)/lethal concentrations (LC) values were estimated. Mussels were individually exposed to allow relatively larger numbers of replicates per treatment. Chronic sulfate exposure significantly reduced growth, foot movement, and relative water content (RWC) in juvenile mussels of M. margaritifera. Mussels at younger stages were not necessarily more sensitive to sulfate. In the acute tests, LC50 of glochidia of M. margaritifera and U. crassus was 1301 and 857 mg/L, respectively. Chronic LC10 was 843 mg/L for 3-week-old U. crassus juveniles, 1051 mg/L for 7-week-old M. margaritifera juveniles, and 683 mg/L for 2-year-old M. margaritifera juveniles. True chronic Lowest Effective Concentration for 7-week-old M. margaritifera may be within the 95% interval of EC10 based on RWC (EC10 = 446 mg/L, 95%CI = 265–626 mg/L). Our study contributed to the understanding of sulfate toxicity to endangered freshwater mussel species in soft water.

Sulfate is a major ion commonly found in natural environments, but excess amounts of it can be harmful to aquatic life. Effects of sulfate on freshwater organisms have been explored previously, but its effects on brackish water biota are poorly known. The elevating human-induced sulfate load to the Baltic Sea necessitates understanding how brackish water species tolerate the additional sulfate. In this study, we conducted chronic sulfate toxicity tests on species from coastal areas of the Baltic Sea. Species of both freshwater and marine origin in the Baltic Sea were tested. Species sensitivity distribution (SSD) with a model-averaging approach was used to derive the fifth percentile hazardous concentration (HC5). For comparison, HC5s were also derived from three alternative single-distribution models. Sulfate sensitivity varied notably between the test species. The most sensitive species were found to be common water moss Fontinalis antipyretica and European whitefish Coregonus lavaretus. The chronic HC5 with 95% confidence interval was 1,204 (472–2,429) mg/L for the coastal Baltic Sea areas, with a salinity range from 2 to 6‰. To account for SSD uncertainties, the HC5 is divided by the assessment factor (AF) to derive the predicted no effect concentration (PNEC). Different AF scenarios were evaluated through deriving the percentages of species affected under each PNEC. The PNEC that would protect over 95% of species with a 95% probability was 469 mg/L, corresponding to an AF of 2.57, which accounted for the statistical uncertainties from the SSD modeling. Compared to species inhabiting freshwater ecosystems in general, the Baltic Sea species showed significantly higher tolerance to sulfate. The toxicity tests performed here on a wide range of Baltic Sea species significantly contribute to the understanding of the sensitivity of brackish water species to sulfate and advanced the development of its risk assessment in brackish water.

Behavioral endpoints have been increasingly used in ecotoxicology for their relevance to individual fitness and ecological effects. However, due to the lack of standard experimental protocols, behavioral endpoints are mostly excluded when deriving environmental quality guidelines. To increase reliability and comparability, behavioral endpoints need to be developed alongside standard endpoints in experiments incorporating elements of standard protocols. In this study, we explored a low-cost methodology to examine the use of activity as a chronic endpoint in a bivalve species in sulphate toxicity tests, following principles of the standard protocol. Adults and juveniles of Baltic clam ( Macoma balthica ) were exposed to sodium sulphate separately. The adult bivalves were individually inspected for their activity at frequent intervals. Activity was at first inhibited, but the extent of activity inhibition decreased and activity EC10 (10% effective concentration) increased as the exposure continued. In M. balthica juveniles, LC10 based on survival was 9001 mg/L sulphate. In M. balthica adults, activity EC10s (1713 − 3176 mg/L) were consistently lower than wet mass EC10 (5511 mg/L). Siphonal autotomy in M. balthica was observed at similar sulphate levels as the activity-based chronic EC10s. We found that the sensitivity of behavioral endpoints in major ion exposures depended on the duration of exposure and, consequently, they need to be evaluated in a case-by-case scenario in the regulatory ecotoxicological context.

Sulfate is a natural major ion commonly found in the environment. Various anthropogenic activities can lead to the discharge of sulfate in high concentrations, causing negative effects on aquatic organisms. While chronic toxicity of sulfate for brackish water species was established, acute toxicity data were scarce. In this study, we tested the acute toxicity of sulfate to seven Baltic Sea species and, together with the literature data, derived the fifth percentile hazardous concentration (HC5) through a species sensitivity distribution (SSD) with 12 species. Acute sulfate sensitivity varied across taxa, with fish and crustaceans being much more sensitive than bivalves, algae, rotifers and bacteria, which led to a bimodal SSD. The most sensitive species tested were whitefish (Coregonus lavaretus) and vendace (Coregonus albula) during fertilization, and the most tolerant were cyanobacterium Synechococcus sp. and bacterium Aliivibrio fischeri. Acute HC5 using the model-averaging approach was 2489 (1016–3990) mg/L sulfate. With a Predicted No Effect Concentration of 1011 mg/L, the upper limit of the 95% confidence interval for the estimated percentage of species affected was below 5%. This new data contributes to the development of the maximum allowable concentration for the sulfate environmental quality standard in the northern Baltic Sea.