Commercial pesticides for urban applications induced population growth and sub-cellular alterations in Raphidocelis subcapitata (Chlorophyceae) at concerning environmental concentrations.

Information regarding the safety and environmental risks of pesticides intended for urban use remains limited. This study aimed to assess the effects of four common pesticides on the microalga Raphidocelis subcapitata: DIAZINON® 25% C. E., Roundup®, URBACIN® 20C. E., and VAPODEL® 20% C. E., which are commercial formulations of diazinon, glyphosate, dichlorvos, and cypermethrin, respectively. According to 96-h inhibition of population growth bioassays, the four pesticide toxicities exemplified the following order: DIAZINON® (diazinon) > Roundup® (glyphosate) > VAPODEL® (dichlorvos) > URBACIN® (cypermethrin). Increasing pesticide concentrations elicited alterations in the specific growth rates (µmax). The macromolecule contents and photosynthetic pigments increased in groups exposed to the highest concentrations of DIAZINON® 25%, Roundup®, and URBACIN® 20 compared to the control group, despite these treatments inducing lower population growth rates. VAPODEL® 20% induced higher growth rates and lower macromolecule content compared to the control. Since active ingredients were not quantified, certain comparisons may prove limiting, but it is important to assess the effects of the whole mixtures in the form that they enter the environment, especially for urban-intended applications or generic formulations with higher additive contents. Finally, this study demonstrated that commercial pesticide formulations designed for urban applications might pose a threat to freshwater microalgae due to their underestimated toxic potential, but further studies are required.

Feeding behavior of early life stages of the zebrafish Danio rerio is altered by exposure to glyphosate.

Glyphosate levels and the transfer of glyphosate across trophic levels have rarely been studied in zooplankton. The food preferences of zebrafish during the first-feeding stage (which is critical for the survival of organisms), were analyzed because of the requirement for live food. Larval survival begins to be affected when glyphosate intake exceeds 0.3666 µg/larvae/day, in the case that only the food is contaminated; if the medium is also contaminated, the effects on survival start from 0.2456 µg/larvae/day. It was shown that glyphosate was more likely to be incorporated through the medium than through the food (zooplankton), which supports the results of previous studies that have ruled out the potential for biomagnification. The bioconcentration factor (BCF) of glyphosate was determined using an ELISA tests specific to measure glyphosate in the fish D. rerio, the rotifers Brachionus calyciflorus and Lecane papuana, and the cladoceran Ceriodaphnia dubia. The experimental design consisted in exposing seven zebrafish adults per replica (four replicates) in three treatments 1, 5, and 10 mg/L of glyphosate for 96 h to obtain bioconcentration factors in the gills, liver, and muscle. These concentrations were selected as potential glyphosate concentrations right after application as double highest reported concentration. Glyphosate levels in zooplankton can represent up to 6.26% of the total weight of rotifers (BFC = 60.35) and in zebrafish adult organs were less than 8 µg/mg of tissue (BCF values < 6). Although glyphosate does not biomagnify, our results suggest that glyphosate affected the dynamics between zooplankton and zebrafish larvae, diminishing survival and feeding rates, given that zooplankton species bioconcentrate glyphosate in large quantities. The BCF values found in this contribution are higher than expected. Glyphosate exposure affected energy metabolism and feeding behavior of zebrafish larvae, which presented high mortality rates at environmentally relevant concentrations.

Toxicity evaluation of cypermethrin, glyphosate, and malathion, on two indigenous zooplanktonic species.

In Aguascalientes, Mexico, there is a special concern about pesticides because of their intensive use on guava production areas, which are located in the vicinity of water reservoirs; thus, non-target organisms could be exposed. Thereafter, the aim of this work was to assess the effect of cypermethrin, Faena® (glyphosate), and malathion, which are the most used pesticides in Aguascalientes' guava production, on the indigenous freshwater species Alona guttata (cladoceran) and Lecane papuana (rotifer). Acute 48-h toxicity tests were carried out, and LC50 values were calculated. Then, five sublethal concentrations (1/80, 1/40, 1/20, 1/10, and 1/5 of the respective LC50) were selected for the chronic assays: (a) intrinsic growth rate analysis in the rotifer and (b) partial life table analysis in the cladoceran. The results of the acute toxicity tests showed that A. guttata was more sensitive to malathion (LC50 = 5.26 × 10-3 mg/L) at concentrations found in natural environments with continuous application on guava fields, whereas L. papuana was more sensitive to Faena® (LC50 = 19.89 mg/L). The somatic growth of A. guttata was inhibited for the chronic exposure to cypermethrin. In addition, cypermethrin and Faena® seemed to exert endocrine disruptive effects on A. guttata. Moreover, malathion chronic exposure significantly decreased the survival of A. guttata. Moreover, L. papuana was affected chronically for the three pesticides.

Energy reserve modification in different age groups of Daphnia schoedleri (Anomopoda: Daphniidae) exposed to hexavalent chromium.

Caloric content is a reliable biomaker of effect since it is modified by exposure to toxicants that can alter basal metabolism. Since organisms' age modifies how energy resources are allocated and modifies the activity of antioxidant enzymes, the response to toxic agents could be altered with age. Seven age groups of Daphnia schoedleri (0, 3, 5, 7, 14, 21, and 28-day-old) were exposed for 24h to two sublethal concentrations of Cr(VI): 1/25 and 1/5 of the 48 h EC(50) of each age group, to determine the age at which susceptibility to Cr(VI) is highest. To evaluate energy content, carbohydrate, protein and lipid reserves were quantified and antioxidant enzymes activity was assessed (SOD, CAT, GPx, and GR). Furthermore, an integrative approach was applied to evaluate both sets of responses and interpret them as a whole in a simply visual way, achieved by the integrated biomarker response approach. Results indicate that Cr(VI) induced significant differences in all age groups. Seven and 14-day-old organisms were exposed to the highest concentrations (based on their EC50) and showed greater tolerance to this metal. Susceptibility to the toxicant was highest in younger specimens in which energy requirements are greater due to high growth rates (basal metabolism), as a result of which more energy reserves are expended to satisfy demands in terms of growth and response to toxicants.

Energy resource reallocation in Daphnia schodleri (Anomopoda: Daphniidae) reproduction induced by exposure to hexavalent chromium.

Cladocerans are able to store energy in the form of macromolecules such as proteins, lipids and carbohydrates. However, their ability to do so depends to a large extent on their physiological and reproductive condition as well as their age. These macromolecules constitute the total caloric reserves of the body and may be modified as a result of environmental stress conditions by either physical or nutritional factors or by exposure to toxic compounds. Neonates of the freshwater cladoceran Daphnia schodleri were exposed to 0.0064, 0.032 and 0.064 mg L(-1) of hexavalent chromium - Cr(VI) - up to age 5, 7, 14, 21 or 28 d. Survival and fecundity of parthenogenetic females was evaluated for 28d (maximum exposure period). Body length and maximum width were determined in specimens of all ages. Caloric content was evaluated in progeny and females within each age group. Female survival was significantly lower with exposure to 0.064 mg L(-1) of Cr(VI) than with other treatments, and negative effects on reproduction were observed from the lowest concentration on. Largest adult size was attained by control specimens towards the end of the observation period, but no significant differences in neonate size occurred between concentrations. Energy content decreased in adults as toxicant concentration increased, but these females allocated a larger amount of energy reserves to their progeny as a possible compensation aimed at ensuring neonate survival in an adverse environment due to toxicant presence. Sublethal concentrations of Cr(VI) modified energy content in D. schodleri, affecting to varying degrees its survival, growth and reproduction.

Age-altered susceptibility in hexavalent chromium-exposed Daphnia schodleri (Anomopoda: Daphniidae): integrated biomarker response implementation.

Daphnia schodleri is a naturally occurring cladoceran in Mexican freshwater bodies and its relative big size and short life cycle allow its use in toxicological bioassays. Generally, life stages at opposite sides of a normal distribution are considered to be the most susceptible and/or sensitive because of several sub-individual level processes, such as ageing, in which antioxidant activity decreases and reactive oxygen species (ROS) cannot be totally neutralized. Most aquatic populations are structured by organisms of different ages, in which physiological and biochemical responses differ (in magnitude) from each other. According to these statements, seven age groups of D. schodleri (0, 3, 5, 7, 14, 21, and 28 d) were exposed to Cr (VI) in both acute and non-lethal bioassays. Results from acute bioassays were used to estimate the chromium LC(50) values for every age group, which ranged from 0.12 to 0.61 mg L(-1), with a normal pattern distribution. Antioxidant enzymatic activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR) was assessed in organisms exposed to two sublethal Cr(VI) concentrations (0.032 and 0.0064 mg L(-1)). Results showed that neonates' antioxidant activity increased with respect to their controls; nevertheless, the same pattern was not seen in the other age groups. Moreover, GPx activities followed a decreasing pattern with respect to their control groups in organisms 3-d and older. In addition, GR activities were barely modified by chromium exposure of neonates, but not in the other age groups; CAT was only modified in younger daphnids. Once the biomarker responses were normalized, it was possible to observe that enzyme participation differed during the life cycle of this cladoceran and, as a result of their decreasing antioxidant activity, relatively old organisms could have lower capability to deal with pro-oxidant toxicants such as Cr(VI).

Microcystis toxigenic strains in urban lakes: a case of study in Mexico City.

Microcystis is a bloom-forming, common cyanobacterium in urban lakes of Mexico City. To assess the presence of potentially cyanotoxin-producing Microcystis, molecular techniques were applied and acute toxicity bioassays were performed with Daphnia magna neonates exposed to cyanobacterial crude extracts. Toxigenic potential of isolated strains was inferred by amplifying the mcyA-Cd genes and their identity as Microcystis was confirmed through the 16S rDNA and phycocyanin operon amplification. Microcystins synthesized under culture conditions were quantified through ELISA. The acute toxicity bioassays revealed that mortality was independent from the cyanotoxin concentration in some strains; this suggests the presence of other metabolites (different from microcystins) that also exerted an important biological effect. Isolated strains had the mcyA-Cd gene and most of them produced variable amounts of microcystins in the culture conditions used, confirming their toxigenic potential. Results warn about possible toxic effect risks for aquatic biota, neighboring areas, visitors and users of these sites, due to the constant presence of these blooms in the studied water bodies.