Biomedical subjects

W P Norwood

Publications and source records attributed to W P Norwood.

10 recordsLinked to original sources

PubMed2006

Chronic toxicity of arsenic, cobalt, chromium and manganese to Hyalella azteca in relation to exposure and bioaccumulation.

Chronic toxicity of As, Co, Cr and Mn to Hyalella azteca can be described using a saturation-based mortality model relative to total-body or water metal concentration. LBC25s (total-body metal concentrations resulting in 25% mortality in 4 weeks) were 125, 103, 152 and 57,900 nmol g-1 dry weight for As, Co, Cr and Mn respectively. LC50s (metal concentrations in water resulting in 25% mortality in 4 weeks) were 5600, 183, 731, and 197,000 nmol L-1, respectively. A hormesis growth response to As exposure was observed. Growth was a more variable endpoint than mortality for all four toxicants; however, confidence limits based on growth and mortality all overlapped, except Cr which had no effect on growth. Mn toxicity was greater in glass test containers compared to plastic. Bioaccumulation of As, Co, Cr, and Mn was strongly correlated with, and is useful for predicting, chronic mortality.

Amphipoda↗

PubMed2006

Saturation models of arsenic, cobalt, chromium and manganese bioaccumulation by Hyalella azteca.

Bioaccumulation of As, Co, Cr and Mn by the benthic amphipod Hyalella azteca in Burlington City tap (Lake Ontario) water was measured in 4-week tests. Bioaccumulation increased with exposure concentration and demonstrated an excellent fit to a saturation model (r(2): 0.819, 0.838, 0.895 and 0.964 for As, Co, Cr and Mn, respectively). The proportion of total body Mn eliminated during a 24-h depuration period decreased as Mn body concentration increased, apparently due to a saturation of the elimination rate. The high maximum body concentration of 116,000 nmol g(-1) appears to result from the saturation of the Mn excretion which is slightly greater than the maximum Mn uptake rate. Elimination rates for As, Co and Cr were not dependent on body concentration. The four elements were not physiologically regulated in Hyalella. Their body concentrations should be good indicators of bioavailability and useful for environmental assessment.

Amphipoda↗

PubMed2006

Reduced metals concentrations of water, sediment and hyalella azteca from lakes in the vicinity of the sudbury metal smelters, Ontario, Canada.

Hyalella azteca (Crustacea: Amphipoda), water and sediments from 12 circum-neutral lakes between Sudbury and North Bay in Ontario, Canada were sampled in August 1998 and analyzed for 10 metals including Cu, Zn, Cd, Ni, Pb, Co, Mo, V, Ba and Ti. Statistical analyses showed that concentrations of the metals in H. azteca, water and sediment differed significantly (ANOVA, P<0.05) among lakes (except for Zn and Pb in H. azteca and Mo in water). There was a trend of declining metal concentration, especially for Cu, Ni and Co (in water, Hyalella and sediment), with distance from the smelters indicating the reduced impact of atmospheric pollution. Metal concentrations of lakes (water) in the Sudbury area were found to be lower compared to data from the 1970s and 1980s indicating an improvement in water quality. Metal concentrations in field-collected amphipods compared favorably with those measured in the laboratory in animals exposed to deep-water sediments, provided metal concentrations were not extremely low (e.g., Pb) and that water chemistry differences (e.g., pH) were taken into account for some metals (especially Cd). In general bioaccumulation of metals in H. azteca was predicted better from surface water than from sediment total metal.

Animals↗

PubMed2004

Re-evaluation of metal bioaccumulation and chronic toxicity in Hyalella azteca using saturation curves and the biotic ligand model.

Bioaccumulation by Hyalella of all metals studied so far in our laboratory was re-evaluated to determine if the data could be explained satisfactorily using saturation models. Saturation kinetics are predicted by the biotic ligand model (BLM), now widely used in modelling acute toxicity, and are a pre-requisite if the BLM is to be applied to chronic toxicity. Saturation models provided a good fit to all the data. Since these are mechanistically based, they provide additional insights into metal accumulation mechanisms not immediately apparent when using allometric models. For example, maximum Cd accumulation is dependent on the hardness of the water to which Hyalella are acclimated. The BLM may need to be modified when applied to chronic toxicity. Use of saturation models for bioaccumulation, however, also necessitates the need for using saturation models for dose-response relationships in order to produce unambiguous estimates of LC50 values based on water and body concentrations. This affects predictions of toxicity at very low metal concentrations and results in lower predicted toxicity of mixtures when many metals are present at low concentrations.

Amphipoda↗

PubMed2002

Metal bioavailability and toxicity through a sediment core.

Sediment cores from Richard Lake near Sudbury, Ontario, were sectioned and analyzed for total metal content, plus metal bioavailability and toxicity to Hyalella azteca (after equilibration with oxygenated overlying water). Strong and similar sediment profiles were observed for Cd, Co, Cu and Ni in the sediment. However, these differed from metal bioavailability profiles (bioaccumulation by Hyalella and metals in overlying water). Bioavailability profiles for Cu also differed from those for Cd, Co or Ni. The deepest sediment layers, deposited prior to industrial development, were non-toxic. Sediment toxicity was attributed to Ni dissolution into overlying water. Moreover, differential bioavailability of Ni in surface and deeper sediment layers was observed. This can affect the interpretation of toxicity data for sediments collected by different methods (e.g. core vs. grab samples). Based on Pb-210 dating and trends in Ni in the core, chronic toxicity of surface sediments from Richard Lake might approach non-toxic levels in about 15 years.

Animals↗

PubMed2001

Quantification of bioavailable nickel in sediments and toxic thresholds to Hyalella azteca.

Bioaccumulation and chronic toxicity of nickel (Ni) to Hyalella azteca in Ni-spiked sediments was strongly affected by the source of sediment used. The total range in LC50s on a sediment concentration basis ranged over 20 fold. Differences in Ni toxicity generally matched differences in Ni bioaccumulation, and toxicity expressed on a body concentration basis varied less than three fold. Body concentrations, therefore, provide a much more reliable prediction of Ni toxicity in sediments than do concentrations in the sediment. Ni in overlying water was also a reliable predictor of Ni toxicity, but only in tests conducted in Imhoff settling cones with large (67:1) water to sediment ratios. Overlying water LC50s for tests in beakers varied 18 fold. Sediment and body concentrations of Ni tolerated by Hyalella were slightly higher in cones than in beakers. Reproduction was not affected significantly by Ni at concentrations below the LC50 and 10-week EC50s for survival and biomass production (including survival, growth and reproduction) were only marginally lower than 4-week EC50s (survival and growth only).

Animals↗

PubMed1999

Sediment toxicity testing using large water-sediment ratios: an alternative to water renewal.

Deterioration of overlying water quality during toxicity tests with benthic invertebrates is a serious problem with some sediments. One solution is periodic renewal of overlying water. However, this is either labour intensive or requires construction and maintenance of special equipment. Furthermore, water renewal has the potential for flushing toxic chemicals out of the test chamber and establishes nonequilibrium conditions between the water and sediment. An alternative is testing under static conditions using atypical test vessels (e.g. Imhoff settling cones) with a large water volume (1 l) overlaying a much smaller sediment volume (e.g. 15 ml). This results in dramatic improvement of overlying water quality compared to standard static toxicity tests. Compared to water renewal, the test method is much simpler, all toxic substances leached from the sediment are retained in the test vessel, and contaminant concentrations in water and sediment have more time to equilibrate. Chronic sediment toxicity tests (10-28 days) have been conducted successfully under these conditions with Chironomus riparius, Hexagenia sp., Hyalella azteca and Tubifex tubifex.

Journal Article↗

PubMed1998

Toxicity and bioaccumulation of thallium in Hyalella azteca, with comparison to other metals and prediction of environmental impact.

Thallium (Tl) is an extremely toxic but little studied metal. For Hyalella azteca exposed in Lake Ontario water, a 25% reduction in survival (the LC25) occurred at about 48 nmol litre(-1) after 4 weeks. Body concentrations of Tl, which were proportional to water concentrations, averaged 290 nmol g(-1) dry mass at the LC25. Growth was reduced at slightly lower concentrations. Concentrations affecting reproduction were variable at < 50% of the LC25. On a water-concentration basis Tl was more toxic than Ni, Cu or Zn, but less toxic than Cd or Hg to Hyalella; toxicity to Pb was similar. On a body-concentration basis, the toxicities of Tl, Cd, Hg and Pb were all similar. Unlike Cd, Tl toxicity and uptake was affected by K concentrations in the water, and not by Ca, Mg, Na or other ions. Toxicity was proportional to uptake, and body concentrations were better predictors of toxicity than water concentrations in media with varying K concentrations. Preliminary measurements of Tl and Cd uptake by Hyalella from Hamilton Harbour and Lake Ontario sediments suggested that total bioavailable metal concentrations were greater in deep-water sediments from Lake Ontario than in sediments from the harbour. The ratio of bioavailable metal to the toxic threshold was slightly higher for Cd than for Tl, but well below 1 for both metals.

Journal Article↗

PubMed1989

Toxicity test procedures for Hyalella azteca, and chronic toxicity of cadmium and pentachlorophenol to H. azteca, Gammarus fasciatus, and Daphnia magna.

Survival, growth, and reproduction of Hyalella azteca were determined under various test conditions. Reproduction by a cohort begins when the amphipods are 5 to 6 weeks old, peaks at 8 to 12 weeks, and then declines due to continuing adult mortality. Full life-cycle tests can be completed in 12 to 14 weeks at 25 degrees C. Reproduction is poor when only artificial plastic substrate is provided. A substrate of cotton gauze results in dramatic improvements in both reproduction and growth. Better reproduction can be obtained by culturing the amphipods in some sediments, but this makes weekly enumeration difficult. Increased mortality during chronic exposure to cadmium was observed at 1 microgram/L for H. azteca and 3.2 micrograms/L for Gammarus fasciatus. Reproduction during longer exposure was not reduced at concentrations lower than those causing increased mortality within six weeks. Chronic toxicity of pentachlorophenol was observed at 100 micrograms/L for both species. Chronic toxicity to Daphnia magna was similar to that of the amphipods for cadmium, but lower for pentachlorophenol. Amphipods are at least as sensitive as Daphnia to a variety of toxicants during chronic exposure.

Animals↗

PubMedDate not supplied

Chronic toxicity and bioaccumulation of 2,5,2',5'- and 3,4,3',4'-tetrachlorobiphenyl and Aroclor 1242 in the amphipod Hyalella azteca.

The addition of 100 micrograms/L of Aroclor 1242 (A1242) or 2,5,2',5'-tetrachlorobiphenyl (TeCB) during 10 week chronic toxicity tests with Hyalella azteca resulted in complete mortality. There were no effects on survival, growth, or reproduction after addition of 30 micrograms/L. Toxic effects were observed at tissue levels of between 30 and 180 micrograms/g on a wet weight basis, and tissue levels appear to be a better indicator of toxicity than levels in water. No toxic effects were observed after additions of up to 2,700 micrograms/L of the coplanar congener 3,4,3',4'-TeCB. H. azteca has the ability to avoid accumulating in excess of 140 micrograms/g 3,4,3',4'-TeCB. The amount taken up was proportional to the amount added in water up to 100 micrograms/L, but was constant at higher additions, possibly accounting for its relatively low toxicity. The low toxicity of the coplanar congener, as compared to the non-coplanar 2,5,2',5'-TeCB, is in direct contrast to the high toxicity of coplanar PCB congeners to mammals and may be associated with slower rates of aromatic hydrocarbon metabolism in amphipods. Polychlorinated biphenyl levels measured in amphipods from Lake Ontario are approximately 100-fold below levels associated with toxicity in H. azteca, but are above levels which, through biomagnification up the food chain, lead to salmonid residues in excess of 2 micrograms/g, a tolerance limit for human consumption.

Animals↗