Effects from log-yard stormwater runoff on the microalgae Scenedesmus subspicatus: intra-storm magnitude and variability

Critical knowledge gaps and relevant variables requiring consideration when performing aquatic ecotoxicity assays

The increasing diversity and complexity of contaminants released in the environment continuously lead to new challenges when applying ecotoxicity assays. This paper comprises a review concerning exposure assessment and highlights important variables that should be taken into account when investigating aquatic media toxicity under both laboratory or field conditions. Thus, to reflect as much as possible what occurs in nature, ecotoxicity assays must carefully consider these variables in their experimental design. This includes contaminant properties, the selected bioindicators and biomarkers, the dose mode/regime, concentration vs. load, exposure to single vs. multiple contaminants and exposure of single vs. multiple species. Many of these, however, are not usually taken into account, leading to critical knowledge gaps in this area, discussed in detail herein.

Electrochemical oxidation of indanthrene blue dye in a filter-press flow reactor and toxicity analyses with Raphidocelis subcapitata and Lactuca sativa

Alternative routes to degrade dyes are of crucial importance for the environment. Hence, we report the electrochemical removal of indanthrene blue by using a boron-doped diamond anode, focusing on the toxicity of the treated solutions. Different operational conditions were studied, such as current density (5, 10, and 20 mA cm-2) and electrolyte composition (Na2SO4, Na2CO3, and NaNO3). Besides, the pH was monitored throughout the experiment to consider its direct influence on the ecotoxicity effects. The highest electrochemical oxidation efficiency, measured as color removal, was seen in the 180 min condition of electrolysis in 0.033 M Na2SO4, applying 20 mA cm-2, resulting in a color removal of nearly 91% and 40.51 kWh m-3 of energy consumption. The toxicity towards Lactuca sativa depends solely on pH variations being indifferent to color removal. While the inhibition concentration (IC50) for Raphidocelis subcapitata increases 20% after treatment (in optimized conditions), suggesting that the byproducts are more toxic for this specific organism. Our data highlight the importance of analyzing the toxicity towards various organisms to understand the toxic effect of the treatment applied.

Phycoremediation potential of microalgae species for ethidium bromide removal from aqueous media

Ethidium Bromide (EtBr) is an organic compound used in molecular biology investigations. EtBr ability of intercalating in the DNA molecule makes it a toxic substance. The objective was to evaluate the phycoremediation potentials of Chlorella vulgaris, Desmodesmus subspicatus and Raphidocelis subcapitata tested separately and in a mixture (Mix) for EtBr removal from the aqueous medium. Experiments were conducted using an initial algae biomass of 10⁶ cell/mL, exposed to 500 µg/L of EtBr. The removal efficiency (µg EtBr L^-1) after 3 h in each treatment were: Mix (72.8 µg.L^-1) >D. subspicatus (48.4 µg.L^-1) >R. subcapitata (24.6 µg.L^-1) >C. vulgaris (19.9 µg.L^-1). However, when EtBr mass reduction per microalgae density is considered (ng.algae^-1), the efficiency ranking changes to: D. subspicatus (1.9 × 10^-5ng.algae^-1) >C. vulgaris (1.4 × 10^-5ng.algae^-1) >Mix (9.8 × 10^-6ng.algae^-1) >R. subcapitata (2.8 × 10^-6ng.algae^-1). The results suggest that initial algal population density is a determinant factor for efficient EtBr removal by microalgae species in short term treatments. In order to obtain 100% of EtBr removal, it should be necessary 10¹⁰, 10¹⁰ and 10¹¹ algae.mL^-1 of C. vulgaris, D. subspicatus and R. subcapitata, respectively. The results strongly suggest phycoremediation can be explored as an alternative method for EtBr removal.

Microalgal whole-cell biomarkers as sensitive tools for fast toxicity and pollution monitoring of urban wet weather discharges

Urban wet weather discharge (UWWD) management is an important issue. UWWD often represents a significant source of pollution in all aquatic bodies. The occurrence of this pollution is difficult to predict due to the variability of storm events and the unknown contents of urban watershed leached out by rain. Previous studies have tried to demonstrate the ecotoxic impact of UWWD. However, most of them merely highlight the limitations of classic monospecific bioassays, given the high dilution of micropollutants or the presence of nutrients masking toxic effects. Overcoming this problem is therefore of great interest. In this study, we demonstrated the utility of a battery of biomarkers (e.g. membrane permeability, chlorophyll fluorescence, esterase and alkaline phosphatase activities) on the microalgae Chlorella vulgaris to detect the toxic effects of 7 UWWD samples after short exposures (2 and 24 h). These biomarkers are linked to microalgal life traits. Complementarily, monospecific bioassays were carried on Pseudokirchneriella subcapitata, Chlorella vulgaris, Daphnia magna and Heterocypris incongruens to compare their sensitivity to the UWWD samples. No toxic effect was detected in any of the bioassays. Yet, algal biomarkers indicated a disturbance in microalgae physiology, and particularly a perturbation of chlorophyll fluorescence, which was observed in all of the samples tested. While algal membrane permeability was affected by only one UWWD, these two enzymatic activities were stimulated or inhibited depending on the sample. Finally, this study demonstrates the sensitivity of algal biomarkers and the need to develop new, fruitful approaches to characterizing UWWD toxicity.

Removal and Biodegradation of 17β-Estradiol and Diethylstilbestrol by the Freshwater Microalgae Raphidocelis subcapitata

Natural steroidal and synthetic non-steroidal estrogens such as 17β-estradiol (E2) and diethylstilbestrol (DES) have been found in natural water, which can potentially endanger public health and aquatic ecosystems. The removal and biodegradation of E2 and DES by Raphidocelis subcapitata were studied in bacteria-free cultures exposed to single and mixture treatments at different concentrations for 96 h. The results showed that R. subcapitata exhibited a rapid and strong ability to remove E2 and DES in both single and mixture treatments by biodegradation. At the end of 96 h, the removal percentage of single E2 and DES achieved 82.0%, 80.4%, 74.6% and 89.9%, 73.4%, 54.1% in 0.1, 0.5, and 1.5 mg·L^-1, respectively. With the exception of the 0.1 mg·L^-1 treatment at 96 h, the removal capacity of E2 was more efficient than that of DES by R. subcapitata. Furthermore, the removal percentage of mixture E2 and DES achieved 88.5%, 82.9%, 84.3% and 87.2%, 71.8%, 51.1% in 0.1, 0.5, and 1.5 mg·L^-1, respectively. The removal percentage of mixed E2 was significantly higher than that of the single E2. The presence of DES could accelerate the removal of E2 from the mixture treatments in equal concentrations. In addition, the removal was mainly attributed to the biodegradation or biotransformation process by the microalgae cells rather than simple sorption and accumulation in the cells. The microalgae R. subcapitata demonstrated a high capability for the removal of the E2 and DES indicating future prospects for its application.

Effect of Medicago sativa L. and compost on organic and inorganic pollutant removal from a mixed contaminated soil and risk assessment using ecotoxicological tests

Several Gentle Remediation Options (GRO), e.g., plant-based options (phytoremediation), singly and combined with soil amendments, can be simultaneously efficient for degrading organic pollutants and either stabilizing or extracting trace elements (TEs). Here, a 5-month greenhouse trial was performed to test the efficiency of Medicago sativa L., singly and combined with a compost addition (30% w/w), to treat soils contaminated by petroleum hydrocarbons (PHC), Co and Pb collected at an auto scrap yard. After 5 months, total soil Pb significantly decreased in the compost-amended soil planted with M. sativa, but not total soil Co. Compost incorporation into the soil promoted PHC degradation, M. sativa growth and survival, and shoot Pb concentrations [3.8 mg kg(-1) dry weight (DW)]. Residual risk assessment after the phytoremediation trial showed a positive effect of compost amendment on plant growth and earthworm development. The O2 uptake by soil microorganisms was lower in the compost-amended soil, suggesting a decrease in microbial activity. This study underlined the benefits of the phytoremediation option based on M. sativa cultivation and compost amendment for remediating PHC- and Pb-contaminated soils.

Methods for evaluating the pollution impact of urban wet weather discharges on biocenosis: A review

Rainwater becomes loaded with a large number of pollutants when in contact with the atmosphere and urban surfaces. These pollutants (such as metals, pesticides, PAHs, PCBs) reduce the quality of water bodies. As it is now acknowledged that physico-chemical analyses alone are insufficient for identifying an ecological impact, these analyses are frequently completed or replaced by impact studies communities living in freshwater ecosystems (requiring biological indices), ecotoxicological studies, etc. Thus, different monitoring strategies have been developed over recent decades aimed at evaluating the impact of the pollution brought by urban wet weather discharges on the biocenosis of receiving aquatic ecosystems. The purpose of this review is to establish a synthetic and critical view of these different methods used, to define their advantages and disadvantages, and to provide recommendations for futures researches. Although studies on aquatic communities are used efficiently, notably on benthic macroinvertebrates, they are difficult to interpret. In addition, despite the fact that certain bioassays lack representativeness, the literature at present appears meagre regarding ecotoxicological studies conducted in situ. However, new tools for studying urban wet weather discharges have emerged, namely biosensors. The advantages of biosensors are that they allow monitoring the impact of discharges in situ and continuously. However, only one study on this subject has been identified so far, making it necessary to perform further research in this direction.

Effects of single and mixed estrogens on single and combined cultures of D. subspicatus and P. subcapitata

This paper investigates the effect of estrone (E1), 17β-estradiol (E2) and 17α-ethinylestradiol (EE2) individually and mixed at equal proportions (1:1:1) on Desmodesmus subspicatus and Pseudokirchneriella subcapitata in single and combined cultures (S+) at different exposure times based on algal growth (in vivo chlorophyll fluorescence and cell counting) and coenobium formation. EE2 and E2 were more toxic to individual and combined (S+) cultures than was E1. The frequency of coenobium formation by D. subspicatus increased significantly for all estrogens and all concentrations. After 96 h, D. subspicatus prevailed in S+. The results of the exposure to E+ suggested a less-than-additive effect on D. subspicatus and S+ and additive effect on P. subcapitata. Toxic effects occurred for both species exposed to E+ with individual estrogen concentrations below the NOEC of each species. Assays must include changes in response due to the exposure of more than one species to more than one estrogen.

Modeling urban storm rainfall runoff from diverse underlying surfaces and application for control design in Beijing

Managing storm rainfall runoff is paramount in semi-arid regions with urban development. In Beijing, pollution prevention in urban storm runoff and storm water utilization has been identified as the primary strategy for urban water management. In this paper, we sampled runoff during storm rainfall events and analyzed the concentration of chemical oxygen demand (COD), total suspended solids (TSS) and total phosphorus (TP) in the runoff. Furthermore, the first flush effect of storm rainfall from diverse underlying surfaces was also analyzed. With the Storm Water Management Model (SWMM), the different impervious rates of underlying surfaces during the storm runoff process were expressed. The removal rates of three typical pollutants and their interactions with precipitation and underlying surfaces were identified. From these rates, the scenarios regarding the urban storm runoff pollution loading from different designs of underlying previous rates were assessed with the SWMM. First flush effect analysis showed that the first 20% of the storm runoff should be discarded, which can help in utilizing the storm water resource. The results of this study suggest that the SWMM can express in detail the storm water pollution patterns from diverse underlying surfaces in Beijing, which significantly affected water quality. The scenario analysis demonstrated that impervious rate adjustment has the potential to reduce runoff peak and decrease pollution loading.

Wastewater generated during cleaning/washing procedures in a wood-floor industry: toxicity on the microalgae Desmodesmus subspicatus

In industries based on dry processes, such as wood floor and wood furniture manufacture, wastewater is mainly generated after cleaning of surfaces, storage tanks and machinery. Owing to the small volumes, onsite treatment options and potential environmental risks posed to aquatic ecosystems due to discharge of these wastewaters are seldom investigated. In the present study, the effects of cleaning wastewater streams generated at two wood floor production lines on Desmodesmus subspicatus were investigated. The microalgae was exposed to different wastewater concentrations (100, 50, 25, 12.5 and 6.25% v:v) and the algae growth evaluation was based on in vivo chlorophyll fluorescence, cell density, cell size (number of cells/colony) and cell ratio (length/width). Inhibitory effects of the tested wastewaters on the microalgae were positively related to concentration and negatively related to exposure time. The EC50,24 h of blade cleaning wastewater (BCW) and floor cleaning wastewater (FCW) were 3.36 and 5.87% (v:v), respectively. No negative effect on cell colony formation was caused by BCW, whereas an increase of 90% unicellular cells was observed in FCW concentrations below 50% (v:v). At the lowest concentration (3.13% v:v) where no growth inhibition was observed, both wastewater streams caused changes in cell dimensions by increasing cell length and width. To conclude, wastewaters generated during cleaning procedures in the wood floor industries can have severe environmental impacts on aquatic organisms, even after high dilution. Therefore, these wastewaters must be treated before being discharged into water bodies.

Stormwater run-off from an industrial log yard: characterization, contaminant correlation and first-flush phenomenon

The stormwater run-off generated in an industrial log yard during eight run-off events was studied with the main focus on the transport of toxic metals. Associations between water quality constituents and potential surrogates were evaluated by correlation analysis. The first-flush phenomenon was verified by normalized M(V) curves. The results have shown that, whereas some metals such as Zn, Ba, Cd, As and Fe were always detected in these waters, others (Cr, Pb, Cu, Ni, V, Co) were not. Large variations in the water constituents' concentrations were observed, with Fe, Pb and V being the most variable ones. Concentrations of Zn and Cu in the run-off waters exceeded the values established by the Swedish environmental authorities in 100% and 97% of samples, respectively. The correlation analyses indicated TSS as a potential surrogate of Pb, V, Co, Ni, As, Ba, Cr and COD (0.949 > R > 0.808), making it reasonable to state that a treatment system with focus on TSS removal would also reduce toxic metals from these waters. The first-flush phenomenon was evident for most of the constituents. Significant differences (p < 0.05) in the first-flush magnitude of different run-off events were observed confirming that hydro-meteorological variables such as dry period, precipitation duration and average intensity play important roles. Metal loads originating from the log yard were mainly composed ofZn, Cu and Ba. Knowledge of the physicochemical characteristics, discharge dynamics and the storm variables involved in the process is a crucial step for the proposal and implementation of a stormwater management programme.