Ecotoxicology of polychlorinated biphenyls in fish--a critical review.

Polychlorinated biphenyls (PCBs) are widespread persistent anthropogenic contaminants that can accumulate in tissues of fish. The toxicity of PCBs and their transformation products has been investigated for nearly 50 years, but there is a lack of consensus regarding the effects of these environmental contaminants on wild fish populations. The objective of this review is to critically examine these investigations and evaluate publicly available databases for evidence of effects of PCBs in wild fish. Biological activity of PCBs is limited to a small proportion of PCB congeners [e.g., dioxin-like PCBs (DL-PCBs)] and occurs at concentrations that are typically orders of magnitude higher than PCB levels detected in wild fish. Induction of biomarkers consistent with PCB exposure (e.g., induction of cytochrome P450 monooxygenase system) has been evaluated frequently and shown to be induced in fish from some environments, but there does not appear to be consistent reports of damage (i.e., biomarkers of effect) to biomolecules (i.e., oxidative injury) in these fish. Numerous investigations of endocrine system dysfunction or effects on other organ systems have been conducted in wild fish, but collectively there is no consistent evidence of PCB effects on these systems in wild fish. Early life stage toxicity of DL-PCBs does not appear to occur at concentrations reported in wild fish embryos, and results do not support an association between PCBs and decreased survival of early life stages of wild fish. Overall, there appears to be little evidence that PCBs have had any widespread effect on the health or survival of wild fish.

Mild maternal stress disrupts associative learning and increases aggression in offspring.

Maternal stress has been shown to affect behaviour of offspring in a wide range of animals, but this evidence has come from studies that exposed gestating mothers to acute or severe stressors, such as restraint or exposure to synthetic stress hormones. Here we show that exposure of mothers to even a mild stressor reduces associative learning and increases aggression in offspring. Female guppies were exposed to routine husbandry procedures that produced only a minimal, non-significant, elevation of the stress hormone cortisol. In contrast to controls, offspring from mothers that experienced this mild stress failed to learn to associate a colour cue and food reward, and showed a greater amount of inter-individual variation in behaviour compared with control offspring. This mild stress also resulted in offspring that were more aggressive towards their own mirror image than controls. While it is possible that these results could represent the transmission of beneficial maternal characteristics to offspring born into unpredictable environments, the potential for mild maternal stress to affect offspring performance also has important implications for research into the trans-generational effects of stress.

Assessment of DNA damage in sperm after repeated non-invasive sampling in zebrafish Danio rerio.

Repeated non-invasive sampling of zebrafish Danio rerio sperm was conducted, sperm counts were obtained and a method for measurement of DNA damage in sperm was developed and validated (single-cell gel electrophoresis, comet, assay). DNA damage in sperm increased with concentration of hydrogen peroxide (H2 O2 , 0-200 µM), and in vitro exposure of sperm to 200 µM H2 O2 produced 88·7 ± 3·9% tail DNA compared to unexposed controls [12 ± 0·7% tail DNA (mean ± s.e., n = 3)]. Frequency of sperm sampling (sampled every 2, 4 or 7 days) did not affect DNA damage in sperm, but sperm counts decreased 57 and 22% for fish sampled every 2 or 4 days, respectively.

Effects of manufactured nanomaterials on fishes: a target organ and body systems physiology approach.

Manufactured nanomaterials (NM) are already used in consumer products and exposure modelling predicts releases of ng to low µg l(-1) levels of NMs into surface waters. The exposure of aquatic ecosystems, and therefore fishes, to manufactured NMs is inevitable. This review uses a physiological approach to describe the known effects of NMs on the body systems of fishes and to identify the internal target organs, as well as outline aspects of colloid chemistry relevant to fish biology. The acute toxicity data, suggest that the lethal concentration for many NMs is in the mg l(-1) range, and a number of sublethal effects have been reported at concentrations from c. 100 µg to 1 mg l(-1). Exposure to NMs in the water column can cause respiratory toxicity involving altered ventilation, mucus secretion and gill pathology. This may not lead, however, to overt haematological disturbances in the short term. The internal target organs include the liver, spleen and haematopoietic system, kidney, gut and brain; with toxic effects involving oxidative stress, ionoregulatory disturbances and organ pathologies. Some pathology appears to be novel for NMs, such as vascular injury in the brain of rainbow trout Oncorhynchus mykiss with carbon nanotubes. A lack of analytical methods, however, has prevented the reporting of NM concentrations in fish tissues, and the precise uptake mechanisms across the gill or gut are yet to be elucidated. The few dietary exposure studies conducted show no effects on growth or food intake at 10-100 mg kg(-1) inclusions of NMs in the diet of O. mykiss, but there are biochemical disturbances. Early life stages are sensitive to NMs with reports of lethal toxicity and developmental defects. There are many data gaps, however, including how water quality alters physiological responses, effects on immunity and chronic exposure data at environmentally relevant concentrations. Overall, the data so far suggest that the manufactured NMs are not as toxic as some traditional chemicals (e.g. some dissolved metals) and the innovative, responsible, development of nanotechnology should continue, with potential benefits for aquaculture, fisheries and fish health diagnostics.

Species-specific impact of microplastics on coral physiology.

There is evidence that microplastic (MP) pollution can negatively influence coral health; however, mechanisms are unknown and most studies have used MP exposure concentrations that are considerably higher than current environmental conditions. Furthermore, whether MP exposure influences coral susceptibility to other stressors such as ocean warming is unknown. Our objective was to determine the physiology response of corals exposed to MP concentrations that have been observed in-situ at ambient and elevated temperature that replicates ocean warming. Here, two sets of short-term experiments were conducted at ambient and elevated temperature, exposing the corals Acroporasp. and Seriatopora hystrix to microspheres and microfibres. Throughout the experiments, gross photosynthesis and net respiration was quantified using a 4-chamber coral respirometer, and photosynthetic yields of photosystem II were measured using Pulse-Amplitude Modulated (PAM) fluorometry. Results indicate the effect of MP exposure is dependent on MP type, coral species, and temperature. MP fibres (but not spheres) reduced photosynthetic capability of Acropora sp., with a 41% decrease in photochemical efficiency at ambient temperature over 12 days. No additional stress response was observed at elevated temperature; photosynthetic performance significantly increased in Seriatopora hystrix exposed to MP spheres. These findings show that a disruption to coral photosynthetic ability can occur at MP concentrations that have been observed in the marine environment and that MP pollution impact on corals remains an important aspect for further research.

Soaking up the oil: Biological impacts of dispersants and crude oil on the sponge Halichondria panicea.

Used during an oil spill to minimise the formation of an oil slick, dispersants have negative biological effects on marine model organisms. However, no study has investigated the impacts of dispersants on adult sponge individuals. Here, we examine the effects of water accommodated oil fraction (WAF - oil in seawater), chemically enhanced WAF (CEWAF - oil and dispersant in seawater) and Benzo[A]Pyrene on sponge Halichondria panicea at physiological and molecular levels. Sponge clearance rate decreased sharply when exposed to WAF and CEWAF but the oil loading at which the clearance rate was reduced by 50% (ED50) was 39-fold lower in CEWAF than in WAF. Transcriptomic analysis revealed a homogenous molecular response with the greatest number of differentially expressed genes identified in CEWAF samples (1,461 genes). Specifically, genes involved in stress responses were up-regulated. This study presents evidence that the use of dispersants should be considered carefully in areas where sponges are present.

Changes in the relative expression pattern of multiple vitellogenin genes in adult male and larval zebrafish exposed to exogenous estrogens.

Production of the lipoprotein vitellogenin (Vg) is induced in fish upon exposure to estrogens and is a biomarker of endocrine disruption in fish. In some fish, three types of Vg (VgA, VgB, and VgC) are recognized and transcribed from at least three distinct Vg genes (vtg). We investigated expression of vtg coding for Vg1A/B, Vg2A/B, and VgC in adult male and larval zebrafish exposed to various estrogenic substances. Quantitative PCR was conducted for transcripts of each vtg and a control gene (beta-actin). Male fish were exposed to 17beta-estradiol (E2) and 17alpha-ethinylestradiol, total RNA was extracted from excised liver, and histopathology of liver, trunk kidney, and gonads was conducted. Larval fish were exposed to 10 different estrogenic substances and total RNA was extracted from groups of whole larvae. In adult male fish, the relative fold change varied, but pattern of expression change (i.e., Vg1A/B > Vg2A/B > VgC) was consistent. Larger males exposed to E2 had significantly higher induction of each vtg. In larval zebrafish, the relative fold change in vtg expression varied according to specific estrogenic substance tested, but the pattern of change (i.e., Vg2A/B > Vg1A/B > VgC) was consistent for each substance that induced vtg.

Gill lesions and death of bluegill in an acid mine drainage mixing zone.

The toxicity of an acid mine drainage (AMD) mixing zone was investigated by placing bluegill (Lepomis macrochirus) at the confluence of a stream contaminated by AMD and a stream having neutral pH. A mixing channel receiving water from both streams was assembled in the field, during July and October 1996, to determine the toxicity of freshly mixed and aged water (2.9-7.5 min). The AMD stream had elevated concentrations of Al and Fe, which precipitated upon mixing, and of Mn, which did not precipitate in the mixing zone. Fish exposed to freshly mixed water had higher mortality than fish exposed to water after aging. Precipitating Al, but not Fe, accumulated on the gills of bluegill, and accumulation was more rapid early during the mixing process than after aging. Fish exposed for 3.5 h to freshly mixed water had hypertrophy and hyperplasia of gill filament and lamellar epithelial cells. Similar lesions were observed after 6.0 h in fish exposed to water aged after mixing. Results demonstrated that Al was the predominant metal accumulating on the gills of fish in this AMD mixing zone, and that mixing zones can be more toxic than AMD streams in equilibrium.

Sub-lethal effects of titanium dioxide nanoparticles on the physiology and reproduction of zebrafish.

There are limited data on the sub-lethal physiological effects of titanium dioxide nanoparticles (TiO(2) NPs) in adult fishes, and the consequences of TiO(2) NP exposure on reproductive success are also unclear. This study aimed to examine the sub-lethal effects of a 14-d aqueous TiO(2) (TiO(2) NP, 0.1 or 1.0 mg l(-1); TiO(2) bulk, 1.0 mg l(-1)) exposure on the physiology and reproductive health of zebrafish. After the 14-d exposure, fish were examined for haematology, whole body electrolyte and trace metal profiles, biochemistry, and histopathology. Then, during a 21-d post exposure recovery period, effects of the TiO(2) exposure on reproductive success were evaluated. Whole body Ti concentrations increased significantly in fish exposed to both the 1.0 mg l(-1) TiO(2) NP and bulk TiO(2) compared to controls, but concentrations returned to control levels by the end of the recovery period. No change in erythrocyte counts were observed, but there was a two-fold decline in leukocyte counts in all TiO(2) treatment groups relative to time-matched controls. Whole body electrolyte and trace metal profiles were not affected by exposure to TiO(2), and there were no changes in Na(+)K(+)-ATPase activity in brain, gill or liver tissues. Total glutathione (GSH) levels in brain, gill and liver tissues were higher in fish exposed to TiO(2) NP (both 0.1 and 1.0 mg l(-1)) compared to bulk TiO(2) and control fish. Histological examination of gill, liver, brain and gonad tissues showed little evidence of treatment-related morphological change. At the end of the 14-d exposure adult zebrafish were able to reproduce; however, the cumulative number of viable embryos produced was lower in fish exposed to 1.0 mg l(-1) TiO(2) (both NP and bulk) by the end of the 21-d recovery period. Overall, this study showed limited toxicity of bulk or nano scale TiO(2) during the exposure; however reproduction was affected in both bulk and NP 1.0 mg l(-1) groups.

Acute toxicity of aromatic and non-aromatic fractions of naphthenic acids extracted from oil sands process-affected water to larval zebrafish.

The toxicity of oil sands process-affected water (OSPW) has regularly been attributed to naphthenic acids, which exist in complex mixtures. If on remediation treatment (e.g., ozonation) or on entering the environment, the mixtures of these acids all behave in the same way, then they can be studied as a whole. If, however, some acids are resistant to change, whilst others are not, or are less resistant, it is important to establish which sub-classes of acids are the most toxic. In the present study we therefore assayed the acute toxicity to larval fish, of a whole acidified OSPW extract and an esterifiable naphthenic acids fraction, de-esterified with alkali: both fractions were toxic (LC50 ∼5-8mgL(-1)). We then fractionated the acids by argentation solid phase extraction of the esters and examined the acute toxicity of two fractions: a de-esterified alicyclic acids fraction, which contained, for example, adamantane and diamantane carboxylic acids, and an aromatic acids fraction. The alicyclic acids were toxic (LC50 13mgL(-1)) but the higher molecular weight aromatic acids fraction was somewhat more toxic, at least on a weight per volume basis (LC50 8mgL(-1); P<0.05) (for comparison, the monoaromatic dehydroabietic acid had a LC50 of ∼1mgL(-1)). These results show how toxic naphthenic acids of OSPW are to these larval fish and that on a weight per volume basis, the aromatic acids are at least as toxic as the 'classical' alicyclic acids. The environmental fates and other toxic effects, if any, of the fractions remain to be established.

Acute and chronic toxicity of fluoxetine (selective serotonin reuptake inhibitor) in western mosquitofish.

Fluoxetine is a biologically active pharmaceutical chemical that has been detected at parts-per-trillion levels in surface waters in North America and Europe. This has generated concern because negative effects in aquatic organisms are possible. Known as a selective serotonin reuptake inhibitor, fluoxetine (e.g., Prozac; Elli Lilly) is neurologically active and widely prescribed for clinical depression in humans. In the present investigation, acute and chronic toxicities of fluoxetine were evaluated in an environmentally relevant species, western mosquitofish Gambusia affinis. Acute toxicity (5 to 5340 ppb fluoxetine) was assessed in neonates (age 24 to 48 hours) exposed in glass aquaria for 7 days; chronic toxicity (0.05 to 5 ppb fluoxetine) was examined in fish exposed from age neonate to age 91 days; and effects of chronic exposure (100 days) on sexual maturation was investigated in mesocosm tanks (100 L) in fish exposed (7 to 71 ppb) from age 59 to 159 days. Acute toxicity of fluoxetine in neonate western mosquitofish was observed to have a 7-day median lethal concentration of 546 ppb. Chronic exposure did not affect survival, growth, or sex ratio; however, increased lethargy in fish exposed to > or =0.5 ppb fluoxetine was observed. In fish exposed from age 59 to 159 days (juvenile to adult life stages), delayed development of external adult sexual morphology was observed at 71 ppb fluoxetine, which consisted of delayed onset of the presence of the black spot in the posterior abdomen in female fish and delayed formation of the elongated anal fin (gonopodium) in male fish. The present study demonstrated that chronic exposure of western mosquitofish to fluoxetine can affect sexual development; however, it does so only at concentrations 3 to 4 orders of magnitude higher than those previously found in the environment.