RESUMEN
Selenium (Se) is an essential micronutrient that becomes toxic when exposures minimally exceed those that are physiologically required. Studies on Se contaminated aquatic environments have identified that embryo-larval fishes are at particular risk of Se toxicity, primarily due to maternal Se transfer to developing eggs during oogenesis. This study emulated these exposures in embryo-larval fathead minnow (FHM), rainbow trout (RBT), white sucker (WSu), and white sturgeon (WSt) using embryonic selenomethionine (SeMet) microinjections. Adverse Se-outcomes observed across these species included spinal and edematous deformities, total individuals deformed, and reduced survival. Spinal deformity was the most sensitive sublethal endpoint and developed at the lowest concentrations in WSt (10 % effects concentration (EC10) = 12.42 µg (total) Se/g dry weight (d.w.)) followed by WSu (EC10 = 14.49 µg Se/g d.w.) and FHM (EC10 = 18.10 µg Se/g d.w.). High mortality was observed in RBT, but SeMet influences were confounded by the species' innate sensitivity to the microinjections themselves. 5 % hazardous concentrations derived across exposure type data subsets were â¼49 % higher when derived from within-species maternal transfer exclusive data as opposed to all, or within-species microinjection exclusive, data. These results support the current exclusion of SeMet microinjections during regulatory guideline derivation and their inclusion when studying mechanistic Se toxicity across phylogenetically distant fishes.
Asunto(s)
Cyprinidae , Selenio , Contaminantes Químicos del Agua , Animales , Selenometionina/toxicidad , Larva , Contaminantes Químicos del Agua/toxicidad , Contaminantes Químicos del Agua/análisis , Peces , Selenio/toxicidadRESUMEN
Selenium (Se) is an essential trace element of concern that is known to contaminate aquatic ecosystems as a consequence of releases from anthropogenic activities. Selenium is of particular toxicological concern for egg-laying vertebrates as they bioaccumulate Se through the diet and deposit excess Se to embryo-offspring via maternal transfer, a process which has been shown to result in significant teratogenic effects. The purpose of the present study was to determine and compare the in ovo effects of Se exposure on early development of a laboratory model fish species native to North American freshwater systems, the fathead minnow (Pimephales promelas), through two different exposure routes, maternal transfer and microinjection. For maternal transfer studies, fathead minnow breeding groups (3 females: 2 males) were exposed to diets containing Se-background levels (1.21 µg Se/g food, dry mass [dm]) or environmentally relevant concentrations of selenomethionine (SeMet; 3.88, 8.75 and 26.5 µg Se/g food dm) and bred for 28 days. Embryos were collected at different time points throughout the study to measure Se concentrations and to assess teratogenicity in embryos. While exposure to dietary Se did not negatively affect fecundity among treatment groups, the lowest treatment group (3.88 µg Se/g food dm) produced on average the most embryos per day, per female. The maternal transfer of excess Se occurred rapidly upon onset of exposure, reaching steady-state after approximately 14 days, and embryo Se concentrations increased in a dose-dependent manner. The greatest concentrations of maternally transferred Se significantly increased the total proportion of deformed embryo-larval fathead minnows but did not impact hatchability or survival. In a second study, fathead minnow embryos were injected with SeMet at concentrations of 0.00 (vehicle control), 9.73, 13.5 and 18.9 µg Se/g embryo dm. Microinjection of SeMet did not affect hatchability but significantly increased the proportion of deformed embryo-larval fish in a dose-dependent manner. There was a greater proportion of deformed fathead minnows at embryo Se concentrations of 18.9 µg Se/g embryo dm when exposed via microinjection versus maternal transfer at concentrations of 28.4 µg Se/g embryo dm. However, the findings suggest that both exposure routes induced analogous developmental toxicities in early life stage fish at Se concentrations between 9.73 and 13.5 µg Se/g embryo dm. Overall, this study demonstrated that microinjection has utility for studying the effects of Se in embryo-larval fish and is a promising method for the study of early life stage Se exposure in egg-laying vertebrates.
Asunto(s)
Cyprinidae/embriología , Embrión no Mamífero/efectos de los fármacos , Exposición Materna , Microinyecciones , Selenometionina/administración & dosificación , Selenometionina/toxicidad , Animales , Antioxidantes/farmacología , Dieta , Ecosistema , Femenino , Agua Dulce , Larva/efectos de los fármacos , Estadios del Ciclo de Vida/efectos de los fármacos , Modelos Lineales , Masculino , Reproducción/efectos de los fármacos , Selenio/análisis , Contaminantes Químicos del Agua/toxicidadRESUMEN
Alberta's oil sands petroleum coke (PC) generation has in recent years surpassed 10 million tonnes. Petroleum coke has been proposed as an industrial-scale sorbent to reduce concentrations of organic chemicals in oil sands process-affected water (OSPW). However, PC contains up to 1000â¯mg of vanadium (V) per kg of PC, and during the treatment it leaches from coke reaching levels of up to 7â¯mg/L in "treated" OSPW. Little information is available on how common water quality variables affect the toxicity of V to aquatic organisms. Here descriptive relationships are presented to describe how site-specific surface water characteristics representative of the Alberta oil sands region influence the toxicity of V to Daphnia pulex. Results revealed that when D. pulex was exposed to an increase in pH, a threshold relationship was found where acute V toxicity increased from a lethal median concentration (LC50) of 1.7 to 1.2â¯mgâ¯V/L between pH 6 and 7 and then levelled off at around 1â¯mgâ¯V/L. When alkalinity (from 75 to 541â¯mg/L as CaCO3) and sulphate (from 54 to 394â¯mg/L) increased, the acute toxicity of V decreased slightly with LC50s changing from 0.6 to 1.6, and from 0.9 to 1.4, respectively. When the length of V exposure was extended (from 2 to 21â¯d), only an increase of sulphate from 135 to 480â¯mg/L caused a slight increase in V toxicity from a LC50 of 0.6 to 0.4â¯mgâ¯V/L, the opposite trend seen in the acute exposures. In addition, the influence of two OSPW representative mixtures of increasing sodium and sulphate, and increasing alkalinity and sulphate on V acute toxicity to D. pulex were evaluated; only the mixture of increasing sodium (from 18 to 536â¯mg/L) and sulphate (from 55 to 242â¯mg/L) caused a slight decrease in V acute toxicity (LC50 1.0-2.1â¯mgâ¯V/L). Evidence is presented that variations in surface water chemistry can affect V toxicity to daphnids, although only to a small degree (i.e. within a maximum factor of 2 in all cases evaluated here). These relationships should be considered when creating new water quality guidelines or local benchmarks for V.
Asunto(s)
Daphnia/efectos de los fármacos , Modelos Teóricos , Yacimiento de Petróleo y Gas , Ríos/química , Vanadio/toxicidad , Contaminantes Químicos del Agua/toxicidad , Alberta , Animales , Coque/análisis , Dosificación Letal Mediana , Petróleo/análisis , Pruebas de Toxicidad Aguda , Pruebas de Toxicidad Crónica , Aguas Residuales/química , Calidad del Agua/normasRESUMEN
Selenium (Se) enrichment has been demonstrated to vary by several orders of magnitude among species of planktonic algae. This is a substantial source of uncertainty when modelling Se biodynamics in aquatic systems. In addition, Se bioconcentration data are largely lacking for periphytic species of algae, and for multi-species periphyton biofilms, adding to the challenge of modelling Se transfer in periphyton-based food webs. To better predict Se dynamics in periphyton dominated, freshwater ecosystems, the goal of this study was to assess the relative influence of periphyton community composition on the uptake of waterborne Se oxyanions. Naturally grown freshwater periphyton communities, sampled from five different water bodies, were exposed to environmentally relevant concentrations of selenite [Se(IV)] or selenate [Se(VI)] (nominal concentrations of 5 and 25⯵g Se L-1) under similar, controlled laboratory conditions for a period of 8 days. Unique periphyton assemblages were derived from the five different field sites, as confirmed by light microscopy and targeted DNA sequencing of the plastid 23S rRNA gene in algae. Selenium accumulation demonstrated a maximum of 23.6-fold difference for Se(IV) enrichment and 2.1-fold difference for Se(VI) enrichment across the periphyton/biofilm assemblages tested. The assemblage from one field site demonstrated both high accumulation of Se(IV) and iron, and was subjected to additional experimentation to elucidate the mechanism(s) of Se accumulation. Selenite accumulation (at nominal concentrations of 5 and 25⯵g Se L-1 and mean pH of 7.5 across all treatment replicates) was assessed in both unaltered and heat-killed periphyton, and in periphyton from the same site grown without light to exclude phototrophic organisms. Following an exposure length of 8 days, all periphyton treatments showed similar levels of Se accumulation, indicating that much of the apparent uptake of Se(IV) was due to non-biological processes (i.e., surface adsorption). The results of this study will help reduce uncertainty in the prediction of Se dynamics and food-chain transfer in freshwater environments. Further exploration of the ecological consequences of extracellular adsorption of Se(IV) to periphyton, rather than intracellular absorption, is recommended to further refine predictions related to Se biodynamics in freshwater food webs.