Incipient Lethal Levels Research Articles

Effect of Chemical Corexit 9527 on28 Day old TILAPIA GUINEENSIS FINGERLINGS

The primary focus of this study is to assess the toxicity of the chemical corexit 9527 to 28 day old fresh water tilapia guineensis fingerlings. The toxicity of the chemical corexit 9527 to 28 day old fresh water tilapia guineensis fingerlings was studied in the static renewal bioassay glass tank, using tap water. The 28 day old tilapia guineensis fingerlings collected from Ikpoba HillRiver, Edo State was used to access lethal concentrations of dispersant corexit 9527. Differential sensitivity of test organisms to corexit 9527 was observed.This was achieved by predictive application. The LC50 is actually used as an estimate of the incipient lethal level which is also called the lethal threshold concentration, asymptotic LC50 or tolerant limit. The incipient lethal level is the concentration at which half the population will die in an indefinite period of time. It is estimated by the LC50 at that timefor which no further toxicity has been observed. This steady state LC50 is theincipient lethal level. In fish tests, this often occurs within 4 days, and this is one rationale behind the 96-hour length for a standard acute fish test.The median lethal concentration LC50 of dispersant corexit 9527 on tilapia guineensis was determinedusing a computerized probit analysis according to the methods of finney. The median lethal concentration, LC50 for the 28 day old tilapia guineensis were 409.71mg/l and 367.20mg/lfor 3 and 4 days respectively.The 28 day old tilapia guineensis showed a high level tolerance to lower concentrations of corexit 9527 and high level toxicity at the highest concentration which recorded 100% mortality even at 24-hour exposure period.

Biochemical changes in certain tissues of Cirrhina mrigala (Hamilton) (Cyprinidae:Cyprniformes) exposed to fenthion

Lebaycid (Fenthion), a common organochloride pesticide shows nontarget effect on the Indian carp, Cirrhina mrigala Hamilton. This study presents a brief report on the impact of incipient lethal levels (1/4th and 1/10th of fenthion on the concentration of substrates (carbohydrates, lipids and proteins) in the four important tissues brain, gill, intestine and liver. Maximum decrease in glycogen level was observed in liver tissue (−54.4/30 days) and minimum in Intestine tissue (−0.86/60days). Maximum decrease in protein levels were observed in brain tissue (−40.9/30days) and minimum in Liver tissue (1.6/60 days). Maximum and minimum decrease in lipid levels were observed in the liver tissue (−51.8/30 days and -0.5/60 days).

Aggregation on the edge: effects of hypoxia avoidance on the spatial distribution of brown shrimp and demersal fishes in the Northern Gulf of Mexico

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 445:75-95 (2012) - DOI: https://doi.org/10.3354/meps09437 Aggregation on the edge: effects of hypoxia avoidance on the spatial distribution of brown shrimp and demersal fishes in the Northern Gulf of Mexico J. Kevin Craig* Florida State University Coastal and Marine Laboratory, 3618 Highway 98, St. Teresa, Florida 32358-2702, USA Present address: Southeast Fisheries Science Center, NOAA National Marine Fisheries Service, 101 Pivers Island Road, Beaufort, North Carolina 28516-9722, USA *Email: kevin.craig@noaa.gov ABSTRACT: The northwestern Gulf of Mexico shelf experiences the largest seasonal hypoxic (dissolved oxygen, DO ≤ 2.0 mg l−1) zone in the western hemisphere. This study uses bottom trawl and hydrographic surveys over 3 yr to quantify low DO avoidance thresholds, patterns of aggregation in nearby oxygenated refuge habitats, and spatial overlap of brown shrimp Farfantepenaeus aztecus and several finfishes on the nearshore Louisiana shelf. On average, DO avoidance thresholds were low (1 to 3 mg l−1) and near incipient lethal levels for similar species, suggesting organisms avoid the lowest, lethal DO levels on the shelf. Avoidance thresholds varied both within and among years, indicating that behavioral responses to low DO are context-dependent and vary in relation to the severity of hypoxia and possibly other factors. Despite the absence of physical barriers to movement, evading organisms aggregated at short distances (1 to 3 km) just beyond the margins of the hypoxic zone, indicating that sublethal and indirect effects of hypoxia are probably most intense within a relatively narrow region along the hypoxic edge. DO avoidance thresholds and patterns of aggregation were similar between brown shrimp, the primary target of the commercial shrimp trawl fishery, and several juvenile and small adult finfishes that comprise most of the bycatch. In addition, spatial overlap between brown shrimp and finfishes was highest in the years when hypoxia was most severe, and this effect was stronger for benthic fishes than for pelagic fishes. These results suggest the potential for enhanced harvest and bycatch interactions along the margins of the hypoxic zone as an indirect effect of hypoxia-induced shifts in spatial ­patterns. Such spatially mediated indirect effects are an important means by which hypoxia ­influences mobile species in the Gulf. KEY WORDS: Eutrophication · Spatial statistics · Avoidance behavior · Bycatch · Catchability · Fishery interactions · Dead zone · Farfantepenaeus aztecus · Mississippi River plume Full text in pdf format PreviousNextCite this article as: Craig JK (2012) Aggregation on the edge: effects of hypoxia avoidance on the spatial distribution of brown shrimp and demersal fishes in the Northern Gulf of Mexico. Mar Ecol Prog Ser 445:75-95. https://doi.org/10.3354/meps09437 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 445. Online publication date: January 20, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Use of the biotic ligand model to predict pulse-exposure toxicity of copper to fathead minnows ( Pimephales promelas)

Concentrations of cationic metals (e.g., Ag, Cd, Cu, Ni, Pb, Zn) and other water quality parameters (e.g., pH, alkalinity, hardness, dissolved organic carbon (DOC) concentration) often cycle daily in surface waters, and the toxicity of the metals to aquatic organisms is altered by variations in those water quality parameters. Consequently, a method is needed to predict the LC50s (median lethal concentrations) of dissolved metals in temporally varying water quality. In this study, we combined the biotic ligand model (BLM), which predicts toxicity of cationic metals across a wide range of water quality conditions, with a one-compartment uptake-depuration (OCUD) model, which predicts toxicity of a chemical at any exposure time in either continuous or time-variable exposures, to test whether we could accurately predict pulse-exposure toxicity of Cu to fathead minnow (FHM; Pimephales promelas) larvae. First, we conducted continuous-exposure toxicity tests to calculate 1- to 96-h Cu LC50s for the FHM larvae. Then we re-parameterized the default Cu BLM for FHM until the corresponding predicted Cu LA50s (medial lethal accumulations at the biotic ligand) collapsed together into a narrow band and also fit the generalized pattern of an OCUD model [i.e., a steeply sloping plot of ln(LA50) versus ln(time) at short exposure times, followed by a gradual approach to an incipient lethal level at longer exposure times]. Next, in 72-h tests, we exposed FHM larvae to 2- or 8-h square-wave pulses of elevated Cu concentration followed by recovery in uncontaminated water for the remaining 22 or 16 h in each of three consecutive 24-h pulse-and-recovery cycles, at pH 6 or 7 in water containing either 0.5 or 2 mEq/L hardness and 0 or 20 mg DOC/L. Using the combined BLM-OCUD model developed from continuous-exposure data, we then predicted the Cu LA50s in the pulse-exposure tests and compared those LA50s to the observed pulse-exposure Cu LA50s. Although predicted pulse-exposure LA50s were within ∼4× of the observed pulse-exposure LA50s, delayed deaths during the recovery phases of the exposures precluded more accurate predictions of pulse-exposure Cu LA50s and, as a consequence, of pulse-exposure dissolved Cu LC50s. We conclude that one global OCUD equation linked to a re-parameterized Cu BLM for FHM can be used to predict the acute toxicity of continuous and pulse exposures of Cu to FHM larvae across a range of water quality conditions; but to improve the accuracy of those predictions, a mechanism must be developed to account for delayed deaths.

Zinc toxicity to the mottled sculpin (Cottus bairdt) in high‐hardness water

The median 96-h lethal zinc concentration (LC50) was 439 microg Zn/L (hardness of 154 mg/L as CaCO3) for feral mottled sculpin (Cottus bairdi), decreasing to a median incipient lethal level of 266 microg Zn/L after 13 d. The 30-d chronic value was 255 microg Zn/L. The acute toxicity-hardness (ln-ln) slope of 1.022 exceeded that of the current U.S. Environmental Protection Agency zinc criteria. The mottled sculpin is the second most sensitive fish species for which toxicity data are available.

Tissue-specific Cu bioaccumulation patterns and differences in sensitivity to waterborne Cu in three freshwater fish: rainbow trout ( Oncorhynchus mykiss), common carp ( Cyprinus carpio), and gibel carp ( Carassius auratus gibelio)

Rainbow trout ( Oncorhynchus mykiss), common carp ( Cyprinus carpio) and gibel carp ( Carassius auratus gibelio) were exposed to copper (1–20 μM) in softened Antwerp City tap water at pH 7.3 ± 0.1 and with a water hardness of 292.4 ± 8.1 mg/L CaCO 3 (Ca 100.8 ± 3.0 mg/L; Mg 11.0 ± 0.2 mg/L). LC50s (96 h) were determined and copper accumulation in gills, liver, and kidney assessed over a 10-day period. Rainbow trout (96 h LC50: 3.3 μM/210 μg/L) were three times more sensitive to Cu exposure than common carp (96 h LC50: 10.4 μM/661 μg/L) and almost seven times more sensitive than gibel carp (96 h LC50: 22.0 μM/1398 μg/L). After 96 h, the incipient lethal level (ILL) was reached for common carp, and by the end of the experiment (>120 h) also for rainbow trout. The ILL was never reached for gibel carp. Survival analysis confirmed the differences in sensitivity shown by the 96 h LC50 values. At 1 μM Cu, the relative risk to die was six to seven times greater for rainbow trout as for common or gibel carp, respectively, while it was 9000 and 19,000 times greater at 5 μM Cu. Only the environmental Cu concentrations contributed significantly ( P < 0.001) to the Time-To-Death (TTD). Tissue Cu concentrations did not relate to TTD. Among species, a clear difference in metal handling was apparent, with high liver residues and liver accumulation rates for the most sensitive species, the rainbow trout, and lower liver but higher kidney residues and kidney accumulation rates for the most resistant species, the gibel carp. Gill concentrations and accumulation rates were lowest in the sensitive rainbow trout.

Accumulation and toxicity of cadmium in the aquatic oligochaete Tubifex tubifex: a kinetic modeling approach.

Heavy metal pollution is a serious threat to ecosystem functioning. Different approaches have been developed to relate the exposure of heavy metals to their accumulation and toxicity. One approach is to relate metal toxicity to the concentrations of the metals in the whole body or a specific target tissue instead of the external exposure concentrations. To test the usefulness of this approach, the relationship between cadmium exposure, accumulation, and toxicity was investigated using an oligochaete worm and kinetic modeling. The uptake and elimination of cadmium by the aquatic oligochaete Tubifex tubifex from the aqueous phase was studied as function of time at different exposure concentrations using both radioactive and non-radioactive cadmium. A two-compartmental pharmacokinetic model was constructed and parametrized by fitting the model to the measured cadmium body concentrations during exposure to different cadmium concentrations. The uptake rate constants were dependent on the cadmium exposure concentration, and this relation could be well-described by incorporation of Michaelis-Menten type uptake kinetics. The toxicity of cadmium was analyzed by determining the lethal exposure concentration associated with a mortality of 50% (LC50) at different time points. LC50 values decreased with increasing exposure time reaching the incipient lethal level after 15 d. Critical body concentrations (CBC) associated with 50% mortality were calculated by combining the model-predicted pharmacokinetic parameters and the measured LC50 values. The predicted mean CBC (0.32 micromol/g wet weight +/- 0.02) was in good agreement with the experimentally obtained CBC for cadmium found in T. tubifex (0.37 micromol/g wet weight +/- 0.07) and appeared to be independent of exposure time and exposure concentration. Our results show that a pharmacokinetic modeling approach provides a tool to link metal exposure to availability, accumulation, and toxicity under variable exposure scenarios taking into account the kinetics of the processes.

Acute and chronic toxicity of zinc to the mottled sculpin Cottus bairdi

The acute and chronic toxicity of zinc to wild mottled sculpin (Cottus bairdi) was measured with 13-d and 30-d flow-through toxicity tests, respectively. Exposure water hardness was 48.6 mg/L as CaCO3 and 46.3 mg/L as CaCO3 in the acute and chronic tests, respectively; pH was slightly above neutral; and temperature near 12 degrees C. The median lethal concentration (LC50) after 96 h was 156 microg Zn/L, but decreased with exposure duration to a median incipient lethal level (ILL50) of 38 microg Zn/L after 9 d, the lowest zinc LC50 reported for any fish species. The 30-d chronic no-effect and lowest-effect concentrations were 16 microg Zn/L (no mortality) and 27 microg Zn/L (32% mortality), respectively. The ILL50 was 32 microg Zn/L. No sublethal growth differences were observed during the chronic test. Analysis of the results from these tests suggested that mottled sculpin may experience acute and chronic toxicity at zinc concentrations lower than any other fish species tested to date. Protection of aquatic communities in stream reaches contaminated by metals seem to require determination of zinc toxicity to lotic species other than trout and other species amenable to aquaculture.

Evaluation of surrogate measures of cadmium, lead, and zinc bioavailability to Eisenia fetida

We evaluated weak-electrolyte (0.1 M Ca(NO 3) 2) soil extractions and ion-exchange membranes coated with a metal chelator as measures of Cd, Pb, and Zn bioavailability in spiked artificial soil by comparing their metal availability estimates to acute lethal toxicity in the earthworm Eisenia fetida. Ca(NO 3) 2 extractions were precisely related to toxicity in all toxicity tests, and enabled the development of time-independent LC 50s (incipient lethal-levels, ILLs) calculated using exposure levels based on extraction data. ILLs with 95% CIs for the Cd, Pb, and Zn toxicity tests were 9.8 (9.4–10.3), 1.16 (1.11–1.22), and 6.33 (6.18–6.49) Ca(NO 3) 2-extractable mmol metal/kg soil, respectively. Mixture toxicity of Cd, Pb, and Zn, assessed using the toxic unit (TU) approach, was 1.35 TU, suggesting additivity. Chelating ion-exchange membrane uptake was variable, and not well related to toxicity. Weak-electrolyte extractions show promise as precise, inexpensive surrogate measures of Cd, Pb, and Zn bioavailability in soil.

Pools as refugia for brown trout during two summer droughts: trout responses to thermal and oxygen stress

In non–drought years (1977, 1985), temperatures and oxygen concentrations from 1 to 14 July at the deepest point in each of five pools in Wilfin Beck were similar with ranges of 12–18° C and 7·8–9·8 mg l–1. TroutSalmo truttawere present in all pools. In drought years (1976, 1983), temperature increased and oxygen concentration decreased as pool size decreased. In the two smallest pools, they were outside the thermal and oxygen limits for trout (ranges for both pools 24–29° C, 1·2–2·5 mg l–1), and trout were absent. Values in a medium–sized pool were close to the incipient lethal levels and a few juvenile trout were present in both drought years. The lowest temperatures and highest oxygen concentrations were recorded in the two largest pools (ranges 20–25° C, 3·6–4·8 mg l–1) and trout of all ages (0+ to adults) were present in both drought years. In these two pools, both temperature and oxygen concentration decreased from the surface to the deepest point in the pool. Trout preferred lower temperatures near the pool bottom rather than higher oxygen concentrations near the surface, but some fish moved towards the surface at night when the pool cooled slightly. These field results were discussed in relation to lethal values recorded for brown trout in the laboratory, and there was general agreement between field and laboratory values. Trout in the drought years occurred at temperatures close to, or below, the incipient lethal value of 24·7° C (+0·5) and also at the highest oxygen concentrations, but only when these were at temperatures below the incipient lethal value.

Acclimation‐induced changes in the toxicity of zinc and cadmium to rainbow trout

AbstractAdults and juvenile rainbow trout exposed for 21 d to sublethal levels of zinc or cadmium exhibited significant changes in their respective incipient lethal levels (ILL). Acclimation resulted in exposure‐dependent changes in both tolerance (ILL concentration) and resistance (time to ILL) in both size classes of fish for each metal. The ILLs for adult rainbow trout exposed to zinc increased from 695 μg/L at 131 h for nonacclimated fish to 2,025 μ/L at 168 h for fish previously exposed to 0.5 ILL (324 μg/L zinc). The ILLs for cadmium‐exposed fish increased from 6 μg/L at 187 h for nonacclimated fish to 122 μg/L at 266 h for fish acclimated to 0.5 ILL (10.2 μg/L cadmium). Similar, although somewhat less dramatic, acclimation responses were observed for juveniles with both zinc and cadmium. Juveniles were found to be approximately three times less sensitive to the toxic effects of the metals than were adult fish.

Toxicity of cobalt and copper to rainbow trout: application of a mechanistic model for predicting survival

We conducted 14-day laboratory toxicity tests with rainbow trout to evaluate, (1) the acute toxicity of Co and Cu, and (2) the effects of selected Co concentrations on the toxicity of Cu in Co/Cu mixtures. A one-compartment, uptake-depuration model was used to estimate incipient lethal levels (ILLs) and quantify differences in lethality responses among the Co-only, Cu-only and Co/Cu exposures. Additionally, we compared mortality percentages observed in Co/Cu mixtures to those predicted from two models of joint toxicity. Co was a slower-acting and less potent toxicant than was Cu. For Co, the ILL for 50% mortality was 346 μg l −1; for Cu, the ILL for 50% mortality was 14 μg l −1. Moreover, in Co/Cu mixtures, Co acted as an antagonist during the first 48–96 h, but later acted as an additive or slightly synergistic toxicant—making it difficult to predict short-term mortality of fish in Co/Cu mixtures. Lethality thresholds for Cu were reduced by 11–26% and 37–45%, respectively, in the presence of 50 and 250 μg l −1 Co, although those differences were not statistically significant. The ordering of ILLs for the metal exposures tested was: 250 μg l −1 Co+Cu>50 μg l −1 Co+Cu>Cu-only>Co-only.

Applications of toxicity curves in assessing the toxicity of diazinon and pentachlorophenol to Lumbricus terrestris in natural soils

Toxicity tests were conducted with Lumbricus terrestris exposed to diazinon in three different natural soil types (Brookston Clay, Fox Sand and Guelph Loam) and to pentachlorophenol (PCP) in Fox Sand. Mortalities were monitored at 2, 4, 8, 16, 24, 48, 96 h, and 5, 7, 14, and 21 d. Toxicity curves ( lc 50/time) were fitted to a one-compartment first-order kinetics (1CFOK) model using non-linear regression analysis to determine incipient lethal levels (ILLs). The 1CFOK model provided a reasonable fit to the observed data for diazinon in all soil types. Toxicity was markedly influenced by soil type, with lowest toxicity in Brookston Clay. The 1CFOK model provided a reasonable fit to the toxicity curve for PCP in Fox Sand up to 14 d, but not for the entire 21-d test period due to increased mortality between 14 and 21 d. The results of this study suggest that toxicity curves and ILLs can be generated from the standard soil toxicity testing protocol by increasing the number of observations taken during the course of a 14-d lethality test.

Earthworm bioassays: Adopting techniques from aquatic toxicity testing

Current theories suggest that the effective concentration of soil contaminants is that fraction that resides in the hydrosphere of soil particles; therefore, parallels may be drawn between toxicity testing in soil, sediment and water. Certain practices and concepts used in aquatic toxicity testing may be adapted into soil toxicity testing procedures and increase the general understanding of the toxicity of soil contaminants. The use of lethality thresholds or incipient lethal levels (ILLs) would increase the accuracy of the estimation of toxicity and kinetics in varying soil types, as well as providing validation for a key bioassay assumption. The use of toxicant kinetics and critical body residues (CBR) in relation to toxicity endpoints may provide a more suitable estimate of toxic dose than the soil concentrations of contaminants, especially for hydrophobic organic chemicals, and also provide a means for both examining the bioavailability of soil contaminants and estimating the influence of modifying factors.

Critical body residues (CBRS): Applications in the assessment of pentachlorophenol toxicity to Eisenia fetida in artificial soil

Acute lethality tests were conducted using Eisenia fetida exposed to pentachlorophenol (PCP) in artificial soil. Mortalities were monitored intensively over the first 24 h, followed by observations every 48 h for the duration of the 28-day test. Toxicity curves were fitted to data using a one-compartment first-order kinetics model (1CFOK) to determine incipient lethal levels (ILLs). PCP residues were determined by gas chromatography after cryoextraction. The 1CFOK model provided a good fit to the observed data. Critical body residues (CBRs) ranged from 0.33 to 2.65 mmol PCP kg −1 wet wt, even though soil concentrations of PCP ranged over three orders of magnitude. The consistency of CBRs regardless of soil concentrations suggests that they may be a useful tool in assessing the toxicity of soil contaminants to earthworms.

Relating oxygen levels in the Newfoundland offshore waters to the physiology of Atlantic cod (Gadus morhua)

During the Northern Cod Science Program (NCSP), dissolved oxygen was measured routinely on oceanographic surveys on the Newfoundland Shelf from 1992 to 1994. A periodic regression was fitted to historical oxygen data to obtain a seasonal mean oxygen content, and divergences (anomalies) from the mean were examined. Anomalies were negative (below the photic zone) in the mid-1930s and 1960s and were lower in the early 1980s when data collection stopped until 1992. When data collection resumed in 1992 the anomalies were the lowest of the whole time series. Positive anomalies were found in the 1950s, early 1970s, and in 1993. Mean percent saturation values (% sO2) were also calculated for the Bonavista transect. In the historical mean for the Bonavista transect the minimum was 80% saturation. This minimum covered about 60% of the shelf from the shore outward. The levels of % sO2 for June, July, and September of 1992 were lower than the historical mean by about 10% sO2. In 1993 the levels were slightly higher than the mean. The lowest % sO2 found on the shelf in 1992 (65% sO2) is close to the published incipient lethal level of 60% sO2.

Assessing the effects of modifying factors on pentachlorophenol toxicity to earthworms: Applications of body residues

AbstractThis study examined the toxicokinetic relationship between critical body residues (CBRs) of pentachlorophenol (PCP) at lethality, soil PCP concentrations, and modifying factors of toxicity such as body size, species, temperature, and soil type during 28‐d bioassays with earthworms. Eisenia fetida (0.2–0.4 g) were exposed to PCP at 15 and 24°C in artificial soil and at 24°C in Brookston clay. Lumbricus terrestris (3.3–4.6 g) and Eudrilus eugeniae (1.5–2.7 g) were exposed in artificial soil at 15 and 24°C, respectively. Soil PCP concentrations ranged from 0 to 6.75 mmol PCP/kg soil (dry weight), and body residues were measured by gas chromatography following cryoextraction of freeze‐dried earthworms. Comparisons of toxicity were made using incipient lethal levels (ILLs) and CBRs at lethality. The equations estimated by nonlinear curve fitting of a one‐compartment, first‐order kinetics model provided a good fit to the observed data for all species, temperatures, and soil types at which tests were conducted. Incipient lethal levels for L. terrestris (0.72 mmol/kg soil) and E. eugeniae (0.63 mmol/kg soil) were similar and significantly higher than those for all E. fetida treatments. Incipient lethal levels for E. fetida exposed to PCP in artificial soil at 15 and 24°C were similar and lower than the ILL for E. fetida exposed to PCP in Brookston clay. The toxicity half‐lives were similar for all E. fetida treatments but were higher than for the larger worms, L. terrestris and E. eugeniae, which were similar. Mean CBRs at lethality for E. fetida tested in artificial soil at 24°C ranged from 0.33 to 0.74 mmol/kg (wet weight) over the range of soil PCP exposure concentrations from 0.12 to 3.75 mmol PCP/kg. Mean CBRs for E. fetida exposed to PCP at 24°C in Brookston clay ranged from 0.51 to 1.59 mmol PCP/kg (wet weight) over the same range of soil PCP concentrations and were not significantly different. Critical body residues for E. fetida (15°C), L. terrestris, and E. eugeniae tested in artificial soil at 2.10 mmol PCP/kg ranged between 0.34 and 0.80 mmol PCP/kg. Residues in surviving worms were either similar to or lower than those in dead worms. Similar CBRs in three species of earthworms differing 10‐fold in body size, and for E. fetida exposed to PCP concentrations ranging over more than two orders of magnitude in two different soil types, demonstrate that body residues can act to more effectively integrate the relationship between test organism, exposure, and mortality than soil toxicant concentrations alone.

The critical thermal limits for the bullhead, Cottus gobio, from three populations in north‐west England

SUMMARY1. The objective was to determine the thermal limits for feeding and survival in the bullhead, Cottus gobio, using juveniles (total length 20–30 mm, live weight 0.5–1.5 g) from one population and adults (50–70 mm, 3.5–5.5 g) from three populations.2. Fish were acclimated to constant temperatures (3, 7, 10, 15, 20, 25 or 27 °C) and the temperature was then changed at a rate of 1 °C /30 min to determine the critical limits for feeding, survival over 7 days (incipient lethal temperature), or survival for 10 min or less (ultimate lethal temperature). The rate of 1 °C/30 min was the optimum value from preliminary experiments, using nine rates from 0.5 °C/48 h to 18 °C h−1. As values for adults were not significantly different between populations, they were pooled to provide arithmetic means (with 95% CL) for the thermal limits at each acclimation temperature.3. Feeding limits increased with acclimation temperature to upper and lower mean values (± 95% CL) of 26.5 ± 0.16 °C and 4.2 ± 0.20 °C for adults, 26.6 ± 0.59 °C and 5.0 ± 0.55 °C for juveniles. Incipient lethal levels defined a tolerance zone within which fish survive indefinitely; upper limits increased with acclimation temperature to a plateau of 27.6 ± 0.22 °C for adults and 27.5 ± 0.47 °C for juveniles, lower limits increased from near 0 °C to 2.5 ± 0.31 °C for adults and 2.7 ± 0.47 °C for juveniles. Ultimate lethal levels increased with acclimation temperature to a plateau of 32.5 ± 0.24 °C for adults and 32.6 ± 0.46 °C for juveniles, whilst the lower limits increased from near 0 to 0.9 ± 0.29 °C. Upper feeding, incipient and ultimate lethal values were significantly lower for juveniles than those for adults at acclimation temperatures &lt; 20, &lt; 20 and &lt; 15 °C, respectively.4. The thermal tolerance of bullheads was slightly lower than that of stone loach, similar to that of juvenile Atlantic salmon and higher than that of brown trout; the thermal limits for feeding were much wider than those for salmon or trout.

Efficacy and role of alum in removal of zebra mussel veliger larvae from raw water supplies

The study had four objectives: (1) to determine if alum in concentrations used by water utilities and industries kills zebra mussel veliger larvae; (2) to determine if alum as a coagulant kills veliger larvae; (3) to determine if the flocculant or the flocculation process affects the survival or settling rate (by entrapment in the floc) of veliger larvae; and (4) to determine if prechlorination affects the efficacy of alum. The results obtained from bioassays for the four objectives were compared to those on jar tests of water samples from Ontario Water Treatment Plants. All experiments were performed in a laboratory on the shore of Lake Erie at Wheatley, Ontario. The main findings for each objective were: (1) that the concentrations of alum used in most water treatment plants (i.e. 10–30 ppm was not sufficient to kill the veliger larvae because the 24-h, LC 50 value was 130.5 ppm with a 24-h incipient lethal level of 100 ppm. However, additions of alum which depressed the pH below 5 caused instantaneous kill of veligers. Therefore, due to the toxicity of both hydrogen ions and alum, significant mortality of veligers will occur in the mixing chamber of alum. (2) The acute toxicity tests suggest that the flocculation process (3-h LC 50 = 76 ppm is significantly ( P ⩽ 0.05) more effective at removing veligers than is the coagulation process (3-h LC 50 = 115 ppm). (3) The role of alum in removal of veligers under standard treatment conditions (i.e. 10–30 ppm alum) appears to be mainly a physical one, with the floc physically removing even living veligers. (4) Prechlorination in combination with alum greatly improves the removal of veligers from raw water supplies over the alum alone. Most veligers remain alive for at least 24 h in the floc at concentrations below 100 ppm. In summary, alum will remove veliger larvae by chemical toxicity in the mixing zones where chemical gradients exist for alum, hydrogen ions, and chlorine and by physical removal through flocculation of both living and dead veligers.

MODELING TOXICITY DUE TO INTERMITTENT EXPOSURE OF RAINBOW TROUT AND COMMON SHINERS TO MONOCHLORAMINE

We evaluated the ability of three mathematical models to predict toxicity to common shiners and rainbow trout during intermittent (pulsed) exposures to monochloramine, based on data from continuous-exposure toxicity tests. If a power term for the exposure-water concentration was included in the models, a concentration × time (Cxt) model and the Mancini uptake-depuration model predicted pulse LC50s to within ±50% of the observed pulse LC50s, for the first four pulses in toxicity tests with 2-h pulse/22-h recovery cycles. Beyond the fourth pulse cycle, though, the pulse LC50s predicted using the Cxt model appeared to diverge considerably from the trend of the experimental pulse LC50s, partly because this model does not predict an incipient lethal level (CILL) for either continuous or intermittent exposures. The Mancini model predicted the CILL moderately well in the common shiner intermittent-exposure test but not in the rainbow trout intermittent-exposure test. The Breck three-dimensional damage-repair model did not predict pulse LC50 or CILL values as well as did the other two models, probably because not enough partial-mortality data were available to parameterize the model adequately. Although the underlying processes appear to be more complex than what these simple models assume, the models may still be adequate for use in regulating a few pulse discharges of monochloramine.