Effects of dietborne cadmium on life history and secondary production of a tropical freshwater cladoceran.

The presence of metals in aquatic environments has increased worldwide. Environmental assessments of metals in freshwater ecosystems presume that toxicity is mainly caused by aqueous exposure, but dietborne exposure (contaminated food) in zooplankton may occur because microalgae carry metal ions through adsorption/absorption of dissolved metal species, resulting in toxic effects once ingested by the animals. However, official regulations for ecotoxicological assays in most countries do not consider the toxic effects caused by dietborne exposure. Here, we provide life history parameters and secondary production of Simocephalus serrulatus (Koch 1841) (Cladocera: Daphniidae) fed with cadmium (Cd) contaminated algae during a 21-day bioassay. The microalgae Chlorophyceae Scenedesmus quadricauda was exposed for 96 h to dissolved Cd concentrations of 0.03; 5.87; 12.27 and 22.27 µg Cd l(-1) (equivalent to 1.6 × 10(-10); 3.2 × 10(-8); 6.7 × 10(-8); 1.2 × 10(-7) mol l(-1)) that resulted in algae internal Cd burdens of 0.004; 0.032; 0.270 and 0.280 pg Cd cell(-1), respectively. Significant toxic effects on life history parameters of S. serrulatus were observed. Time of embryonic development, generation time and age at first reproduction (primipara) showed significant delay. Length at first reproduction, number of eggs and clutches produced per female, hatching percentage, body length, survival and feeding rates were significantly reduced. Secondary production, that is, accumulated biomass for growth and reproduction, decreased significantly with dietborne Cd concentrations. Our results emphasize that food can be an important source of metals to zooplankton in aquatic ecosystems. Environmental regulations should consider the diet in ecotoxicological assessments. Furthermore, secondary production may be considered as a suitable endpoint in ecotoxicity tests.

Effects of dietary copper on life-history traits of a tropical freshwater cladoceran.

Life-history parameters of Ceriodaphnia cornuta (Cladocera: Daphniidae) fed on Pseudokirchneriella subcapitata (Chlorophyceae) exposed to different copper concentrations were investigated. C. cornuta individuals were reared in four treatments: (a) reconstituted water and non-contaminated algae (RW); (b) reconstituted water and copper-contaminated algae with either 1.28 × 10(-13) (10(-7)Cu) or (c) 1.93 × 10(-13) g Cu cell(-1) (10(-6)Cu); and (d) natural water from a local reservoir and non-contaminated algae (NW). Copper content in C. cornuta individuals increased as diet-borne exposure increased (RW < 10(-7)Cu < NW < 10(-6)Cu), except for NW individuals, which exhibited higher copper body burden than RW and 10(-7)Cu individuals, suggesting that some copper was available in the natural water. The results suggest that subacute levels of dietary copper stimulated C. cornuta's growth and reproduction, whereas organisms reared on reconstituted water showed nutritional deficiency. Depending on copper exposure concentration, either growth (lower Cu concentration) or reproduction (higher Cu concentration) was further stimulated, suggesting that an alteration of resource allocation is involved in diet-borne copper exposure. Because differences among treatments were only significantly different after day 12 of the experiment, our results reinforce that full life-cycle tests are more appropriate than the standard 7 day or three-brood chronic bioassays used to evaluate dietary copper effects at low, chronic copper inputs and that the use of standard test-organisms may not address site-specific situations for tropical environments.

The effects of Anabaena spiroides exopolysaccharides on copper accumulation in an aquatic food chain.

The influence of Anabaena spiroides exopolysaccharides (EPS) on copper speciation (total dissolved, particulate and free Cu(2+) ions) and bioavailability in aquatic organisms was investigated. Bacteria were used as the first trophic level, Paramecium caudatum (protozoan) as the second and the copepod cyclopoid Metacyclops mendocinus as the third level. The organisms were obtained from a freshwater reservoir and held under continuous laboratory controlled conditions. Freshwater media containing EPS excreted by A. spiroides (10mgL(-1)) and copper (1.0x10(-6)molL(-1)) were used for bacteria growth. Contamined bacteria were used as food source to protozoan, which was further furnished to copepods. The results showed a reduction of EPS concentration during bacteria growth and also a smaller copper accumulation by microorganisms in the presence of EPS. We concluded that A. spiroides exopolysaccharides have reduced copper entrance into the experimental aquatic microbial food chain.

Natural DOM affects copper speciation and bioavailability to bacteria and ciliate.

This study aimed to investigate the influence of natural dissolved organic materials (DOM) on copper speciation (total dissolved, particulate, and free Cu2+ ions) and bioavailability during a two-level experimental microbial food chain. Bacteria were used as the first trophic level, and Paramecium caudatum (protozoan) as the second. The organisms were obtained from a freshwater reservoir and kept under controlled laboratory conditions. Three experimental treatments were performed: exposure of the organisms to copper in the absence of DOM, exposure to DOM in the absence of copper, and exposure to both copper and DOM. Freshwater medium containing natural DOM and copper at a total dissolved concentration of 1.8 x 10(-6) mol L(-1) was furnished to bacteria, which was further used as food to the protozoan. The results showed that after bacterial growth, DOM concentration decreased as quantified by total organic carbon determinations. At the same time, free Cu2+ ions concentration increased in the medium. A lower copper concentration was detected in both microorganisms in the presence of DOM. We conclude that natural DOM reduced copper accumulation in the organisms on the first and second trophic levels, thus reducing the entrance of copper into the aquatic microbial food chain.

The effects of humic substances on copper toxicity to Ceriodaphnia silvestrii Daday (Crustacea, Cladocera).

A major question in the field of ecotoxicology is how DOM affects copper accumulation and toxicity in planktonic organisms; copper acute toxicity and bioaccumulation in Ceriodaphnia silvestrii were investigated in the presence and absence of humic substances (HS) under controlled laboratory conditions. Copper was determined as free Cu2+ ions in the media and total copper in the animals; metal ion buffers were used for ion selective electrode calibration, extending the lower detection limit to 10(-11) mol l(-1). Groups of 20 adult females of similar sizes were exposed (24 h) to a range of nominal copper concentrations. Based on total added copper, LC50 was 4.4 x 10(-8) mol l(-1) without HS, whereas with 20 mg l(-1) HS, it was 25 times higher (1.1 x 10(-6) mol l(-1)). Based on free Cu2+ ions LC50 was statistically similar either with (2.8 x 10(-8) mol l(-1)) or without HS (3.3 x 10(-8 )mol l(-1)). The present results showed that natural DOM reduced copper toxicity and that free Cu2+ ions correlates to the bioavailable fraction to zooplankton. Nevertheless, copper bioaccumulation by C. silvestrii was similar either in the presence or absence of humic substances, suggesting that C. silvestrii regulates its body copper content up to 3.0 x 10(-8) mol l(-1) free Cu2+ ions in the media. The organisms were not able to deal with higher free Cu2+ ions concentrations in the media.