Impact of aquatic humic substances on speciation and toxicity of arsenic and cobalt to Ceriodaphnia dubia

Humic substances (HS) interact with trace metals such as As and Co, affecting their mobility and availability in aquatic systems. However, their combined effects on toxicity to aquatic organisms are not totally understood. The objective of this study was to evaluate the toxicity of Co(II) and As(III) to the water flea Ceriodaphnia dubia in the presence of HS, considering element speciation. Toxicity assays were performed in the presence and absence of HS at two different concentrations of As(III) (10 and 20 μg/L) and Co(II) (50 and 100 μg/L). The free As(III) and Co(II) (< 1 kDa, fraction most potentially bioavailable) in the test solutions were determined via ultrafiltration. While free Co(II) decreased by approximately 80% in the presence of HS, free As(III) decreased just by 1%. Despite the higher percentage of As(III) potentially bioavailable, the presence of HS reduced significantly the toxicity of As at 20 μg/L (no toxicity was observed at 10 μg/L). This was attributed to direct effects of HS such as hormesis, hormone-like effects of HS and/or formation of protective coating. These effects also stimulated the reproduction, including in the assays in the absence of As and Co. HS reduced the toxicity of Co(II) at both test concentrations. The results of this investigation support that HS should be considered when safe limits for As and Co are defined.

Analysis of vitellogenin by histochemical method as an indicator of estrogenic effect in male Danio rerio exposed to metals

Several chemicals present in the aquatic environment have the ability to alter the endocrine system of aquatic organisms, including the metals cadmium (Cd) and zinc (Zn). In males, a tool to analyze this effect is the vitellogenin (VTG) detection, a protein with defined function in the yolk production and subsequent aid to embryo-larval development. This protein is produced just by females and can be detected by simple and cheap methods such as histochemical method. Thus, this study aimed to analyze the capacity of Cd and Zn to induce VTG production in Danio rerio males and determine whether the histochemical labeling method is efficient to study estrogenic effects in this species. For this, D. rerio adult males were exposed chronically (21 days) to 0.25 and 1 μg/L of Cd and 120 and 180 μg/L of Zn, values allowed by the Brazilian and American legislation to aquatic life protection. After which, the organisms were submitted to a histological process as preparation to liver VTG marking by histochemical method and subsequent qualitative analysis of this protein in zebrafish's liver. After analyzes, it was possible observed that Cd and Zn are capable of inducing VTG production in D. rerio males and that the histochemistry method is efficient for detection of estrogenic effects in this species.

The Effects of Sediment Classification Pattern on a Water Column Organism, Ceriodaphnia dubia

The sediment compartment stands out because it functions as both a temporary sink of pollutants and a potential source of these elements that may become available to the water column.This study aimed to correlate the concentrations of total metals in the crude sediment and in the interstitial water with the ecotoxicity in the water column using an a modified sediment ecotoxicity test with Ceriodaphnia dubia. The results indicate that the sediment may contribute to the toxicity in the water column and that such toxicity is possibly not related to the metals present. Based on the chemical analysis of the metals, the Canadian Sediment Quality Guidelines (SQGs) would frame the sediment as non-toxic to benthic organisms, but the SQGs have no reference standards for possible effects on nektonic organisms. Due to the complexity of this compartment, it is fundamental to evaluate the interactions of the different pollutants in the system and possible effects on the nektonic organisms.

Toxicity assessment of arsenic and cobalt in the presence of aquatic humic substances of different molecular sizes

The release of contaminants in aquatic ecosystems can be influenced by humic acids. In this study, toxicity tests using environmentally relevant concentrations of arsenic and cobalt were conducted both in the presence and absence of aquatic humic substances (AHS) and the fractions of different molecular sizes in the range of (<5, 5-10;10-30; 30-100 and >100kDa) using the microcrustacean Ceriodaphnia dubia. AHS together with arsenic reduced the toxicity, and the toxicity decreased in fractions of larger molecular size AHS. Despite the presence of cobalt, the reduction in toxicity was not observed and that depended on the molecular size of AHS. There was a trend of enhanced toxicity for Co in fractions of larger molecular sizes, opposed to that found for arsenic. Thus, the humic substances alter toxicity of trace elements, and this effect varies depending on the size of the humic substances.

Remediation efficiency of three treatments on water polluted with endocrine disruptors: Assessment by means of in vitro techniques

Chemical substances with potential to disrupt endocrine systems have been detected in aquatic environments worldwide, making necessary the investigation about water treatments able to inhibit such potential. The present work aimed to assess the efficiency for removing endocrine disruptors (with estrogenic and androgenic activity) of three simple and inexpensive substrates that could be potentially used in sectors or regions with limited resources: powdered activated carbon (PAC), powdered natural zeolite (ZEO) (both at a concentration of 500 mg L^-1) and natural aquatic humic substances (AHS) (at 30 mg L^-1). MilliQ-water and mature water from fish facilities (aquarium water, AW), were artificially spiked with 17β-estradiol (E2), 17α-ethinylestradiol and dihydrotestosterone. Moreover, effluent samples from waste water treatment plants (WWTP) were also submitted to the remediation treatments. Estrogenic and androgenic activities were assessed with two cell lines permanently transfected with luciferase as reporter gene under the control of hormone receptors: AR-EcoScreen containing the human androgen receptor and HER-LUC transfected with the sea bass estrogen receptor. PAC was efficiently removing the estrogenic and androgenic compounds added to milliQ and AW. However, androgenic activity detected in WWTP effluents was only reduced after treatment with ZEO. The higher surface area of PAC could have facilitated the removal of spiked hormones in clean waters. However, it is possible that the substances responsible of the hormonal activity in WWTP have adsorbed to micro and nanoparticles present in suspension that would have been retained with higher efficiency by ZEO that show pores of several microns in size.

A comparative study of different diets to optimize cultivation of Hyalella azteca in the laboratory

The aim of this study was to assess the influence of four diets on the laboratory cultivation of H. azteca, seeking to improve production of young specimens through reduced mortality and better growth and number of offspring per couple. The best diet was composed of a mixture of diluted commercial fish food, diluted yeast and primrose oil, associated with fish food flakes containing spirulina. With this diet the maximum mortality was 25 percent (at the end of 28 days), the average number of offspring/couple was 11.4 ± 2.8 (at the end of twelve days) and the peak weight and length of the males (at the end of 40 days) were 0.930 μg and 5.26 ± 1.1mm, respectively.

The toxic potential of aldrin and heptachlor on Danio rerio juveniles (Cypriniformes, Cyprinidae)

With the objective of evaluating the effects of organochlorine pesticides (aldrin and heptachlor) on the survival, growth and gill morphology of juvenile zebrafish (Danio rerio), four partial chronic toxicity bioassays were conducted (seven days' duration) with both compounds in a semi-static system with renewal every 24 h. The results did not show any effects on the fish's survival, but did on their growth and gill morphology. Aldrin was more toxic than heptachlor, since the chronic value (CV) for growth was nearly 8.7 times less, a result confirmed by analyzing the histology of the gills, in which the changes detected were considered more severe for the former substance. In general, they were found branchial lesions of first stage, in other words, cell proliferation between the secondary lamellae, hyperplasia, lifting of respiratory epithelial cells; fusion of several secondary lamellae and dilation of blood vessels. Aneurysms (alterations of second stage) they were verified in the exposed organisms to the aldrin, which also presented about 10% of reduction in the standard length and 30% of reduction in the total weight in relation to the exposed organisms to the control. For heptachlor these values were of 8% and 25%, respectively. The intensity of the gill lesions and growth of the fish did not depend on the pesticide concentration, suggesting different modes of action of the products.

Limnological and ecotoxicological studies in the cascade of reservoirs in the Tietê river (São Paulo, Brazil)

An evaluation was made of the quality of samples of water and sediment collected from a series of reservoirs in the Tietê River (SP), based on limnological and ecotoxicological analyses. The samples were collected during two periods (Feb and Jul 2000) from 15 sampling stations. Acute toxicity bioassays were performed using the test organism Daphnia similis, while chronic bioassays were carried out withCeriodaphnia dubia and Danio rerio larvae. The water samples were analyzed for total nutrients, total suspended matter and total cadmium, chromium, copper and zinc concentrations, while the sediment samples were examined for organic matter, granulometry and potentially bioavailable metals (cadmium, chromium, copper and zinc). The results obtained for the limnological variable, revealed differences in the water quality, with high contribution of nutrients and metals for Tietê and Piracicaba rivers, besides the incorporation and sedimentation, consequently causing a reduction of materials in Barra Bonita reservoir, thus promoting the improvement of the water quality in the other reservoirs. The toxicity bioassays revealed acute toxicity for Daphnia similis only in the reservoirs located below Barra Bonita dam. On the other hand, chronic toxicity for Ceriodaphnia dubia and acute for Danio rerio showed a different pattern, decreasing in magnitude from Barra Bonita to Três Irmãos, demonstrating an environmental degradation gradient in the reservoirs.