Extrapolation for Terrestrial Vertebrates

Risk assessment for terrestrial birds and mammals is most usually conducted for pesticides in standardized systems based on results of limited tests required for regulatory approval. Increasingly, attempts at risk assessment are being made for other chemicals. Typically for pesticides, dietary tests are extrapolated to a few representative species and risk factors derived as ratios against modeled environmental concentrations. There has been criticism of the validity of some of the standard tests, which makes even this simple approach difficult to justify. Attempts have been made to extrapolate from those values considered more reliable using statistical approaches. Relative sensitivity of test species has been determined. However, reliable extrapolation from laboratory to field remains elusive. Statistically derived values from test results probably generate extremely conservative estimates of environmental no-effect levels. Substantial information on the biology, distribution and food preference of species has, thus far, barely been applied to risk assessment. Other promising approaches, such as species differences in metabolic capacity, population dynamics models, and even sublethal effects on reproductive or behavioural endpoints, cannot in themselves provide simple risk factors either. A simple approach to generate approximate or relative risk factors is explored. While the accumulation of a set of circumstantial evidence might not be regarded as risk assessment in the normal sense, it might offer us a means to extrapolate to a reasonable understanding of likely effects in the field and contribute to a weight-of-evidence approach that informs risk management. It also focuses further studies to those areas and species within the environment most likely to be adversely affected     

Using Human Data to Develop Risk Values

One of the criticisms of industry-sponsored human subject testing of toxicants is based on the perception that it is often motivated by an attempt to raise the acceptable exposure limit for the chemical. When Reference Doses (RfDs) or Reference Concentrations (RfCs) are based upon no-effect levels from human rather than animal data, an animal-to-human uncertainty factor (usually 10) is not required, which could conceivably result in a higher safe exposure limit. There has been little in the way of study of the effect of using human vs. animal data on the development of RfDs and RfCs to lend empirical support to this argument. We have recently completed an analysis comparing RfDs and RfCs derived from human data with toxicity values for the same chemicals based on animal data. The results, published in detail elsewhere, are summarized here. We found that the use of human data did not always result in higher RfDs or RfCs. In 36% of the comparisons, human-based RfDs or RfCs were lower than the corresponding animal-based toxicity values, and were more than 3-fold lower in 23% of the comparisons. In 10 out of 43 possible comparisons (23%), insufficient experimental animal data are readily available or data are inappropriate to estimate either RfDs or RfCs. Although there are practical limitations in conducting this type of analysis, it nonetheless suggests that the use of human data does not routinely lead to higher toxicity values. Given the inherent ability of human data to reduce uncertainty regarding risks from human exposures, its use in conjunction with data gathered from experimental animals is a public health protective policy that should be encouraged.     

Mysids in toxicity testing — a review

The use of mysid shrimp, particularly the genusMysidopsis, along with specific testing procedures, has become accepted in aquatic toxicology. Investigators have developed methodologies for both culture and testing of these organisms. Acute and chronic (life cycle) toxicity tests in addition to dredge spoil and effluent tests with mysids are now becoming common. Attempts have been made to use mysids as test organisms in behavioral, physiological, nutritional, and food-chain studies. In general,Mysidopsis spp. have been shown to be as sensitive or more sensitive to toxic substances than other marine species tested. The ease of handling and culture, relative sensitivity to toxicants, short life cycle, small size and direct larval development make these organisms desirable for research purposes. Continued research using mysid species will probably demonstrate even greater usefulness of these organisms in assessment of pollutant impacts on estuarine or marine communities.     

Use of Toxicological Data in Estimating Reference Values for Risk Assessment

A number of programs within the U.S. Environmental Protection Agency (USEPA) currently set less-than-lifetime exposure limits in addition to the chronic reference dose (RfD) and reference concentration (RfC). A review of procedures within the USEPA for setting reference values suggests that less-thanlifetime reference values should be more routinely developed and captured in the USEPA's online IRIS database where chronic RfDs and RfCs, as well as cancer slope factors, are currently available. A review of standard testing study protocols was conducted to determine what data were available for setting acute, short-term, and longer-term reference values, as well as chronic values. This review was done from the point of view of endpoints assessed for specific organ systems (both structural and functional), life stages covered by exposure and outcome, durations of exposure covered and the outcomes evaluated for each, and evaluation of latency to response and/or reversibility of effects. This review revealed a number of data gaps and research needs, including the need for an acute and/or short-term testing protocol that can be used to set acute and shortterm reference values, a strategy for when to conduct more extensive testing based on initial screening data or other information (e.g., chemical class, pharmacokinetics, mode of action), additonal standard testing guidlines protocols to allow more complete assessment of certain organ systems and life stages, development of pharmacokinetic data for different life stages, toxicity related to aging, and latency to response, particularly long-term latency as a result of developmental exposures. The implications of this review are discussed relative to characterizing hazard data for setting reference values, and the potential effects on uncertainty factors and low-dose extrapolation.     

Probabilistic Risk Assessment and Risk Mapping of Sediment Metals in Sydney Harbour Embayments

Sediment metal concentrations in embayments of Sydney Harbour, acquired from the literature and from samples collected for this study, were used to generate contaminant probability density distributions using AQUARISK. The sediment metal concentrations often exceeded Australia's interim sediment quality guidelines. Similarly, estuarine spiked sediment toxicity test literature provided adverse biotic effects concentration data to generate species sensitivity distributions using AQUARISK. Although the harbor is subject to other inorganic and organic contamination, we have used sediment metals to demonstrate an approach for ecological risk mapping and environmental management prioritization. Sufficient spiked sediment toxicity test data were found for only three metals—Cd, Cu, and Zn—and some tests were likely to overestimate toxicity. The estimates of the hazardous concentration to 5% of species (the 50th percentile of the 95% species protection level) were 5, 12, and 40 mg/kg DW of total sediment metal for Cd, Cu, and Zn, respectively. These values were generally low when compared with the interim sediment quality guidelines due to the overestimation of toxic effects in the literature data. The parameters for the species sensitivity distributions have been combined with the measured sediment metal concentrations in Homebush Bay to generate risk maps of the estimated species impact for each metal as well as for all three metals collectively assuming proportional additivity. This has demonstrated the utility of comparing contaminants on a consistent scale—ecological risk.     

Can Amphipod Behavior Help to Predict Chronic Toxicity of Sediments?

Amphipods are widely used in both acute and chronic (sub-lethal) sediment tests. Acute sediment tests provide relatively rapid results, but may fail to detect moderately toxic contaminants that are bound to the sediment, whereas chronic life-cycle tests are rarely performed as they are time consuming and expensive. Observations during chronic testing of oil-contaminated sediment suggested that there may be a link between the behavior of the marine amphipod Corophium volutator and reduction in growth rate. Behavior tests were performed with six individual amphipods per treatment using sediment spiked with weathered Forties oil with burrowing time, re-emergence from sediment, and activity prior to burrowing as endpoints. Further behavior tests were used to predict the chronic toxicity of sediments spiked with three crude oils each with a dominant unresolved complex mixture of hydrocarbons (UCM). The effect of sediment type on behavior was also investigated. The results suggested that although the behavior test could not be used alone as a viable alternative to sediment toxicity tests, it could prove useful as an adjunct to acute tests, and help select sediments that deserve further investigation.     

Multi-linear regression analysis, preliminary biotic ligand modeling, and cross species comparison of the effects of water chemistry on chronic lead toxicity in invertebrates

The current study examined the chronic toxicity of lead (Pb) to three invertebrate species: the cladoceran Ceriodaphnia dubia, the snail Lymnaea stagnalis and the rotifer Philodina rapida. The test media consisted of natural waters from across North America, varying in pertinent water chemistry parameters including dissolved organic carbon (DOC), calcium, pH and total CO(2). Chronic toxicity was assessed using reproductive endpoints for C. dubia and P. rapida while growth was assessed for L. stagnalis, with chronic toxicity varying markedly according to water chemistry. A multi-linear regression (MLR) approach was used to identify the relative importance of individual water chemistry components in predicting chronic Pb toxicity for each species. DOC was an integral component of MLR models for C. dubia and L. stagnalis, but surprisingly had no predictive impact on chronic Pb toxicity for P. rapida. Furthermore, sodium and total CO(2) were also identified as important factors affecting C. dubia toxicity; no other factors were predictive for L. stagnalis. The Pb toxicity of P. rapida was predicted by calcium and pH. The predictive power of the C. dubia and L. stagnalis MLR models was generally similar to that of the current C. dubia BLM, with R(2) values of 0.55 and 0.82 for the respective MLR models, compared to 0.45 and 0.79 for the respective BLMs. In contrast the BLM poorly predicted P. rapida toxicity (R(2)=0.19), as compared to the MLR (R(2)=0.92). The cross species variability in the effects of water chemistry, especially with respect to rotifers, suggests that cross species modeling of invertebrate chronic Pb toxicity using a C. dubia model may not always be appropriate.     

The Need for Multiple Lines of Evidence for Predicting Site-Specific Ecological Effects

The goal of this paper is to illustrate the value and importance of the “weight of evidence” approach (use of multiple lines of evidence from field and laboratory data) to assess the occurrence or absence of ecological impairment in the aquatic environment. Single species toxicity tests, microcosms, and community metric approaches such as the Index of Biotic Integrity (IBI) are discussed. Single species toxicity tests or other single lines of evidence are valuable first tier assessments that should be used as screening tools to identify potentially toxic conditions in a effluent or the ambient environment but these tests should not be used as the final quantitative indicator of absolute ecological impairment that may result in regulatory action. Both false positive and false negative predictions of ecological effects can occur due to the inherent variability of measurement endpoints such as survival, growth and reproduction used in single species toxicity tests. A comparison of single species ambient toxicity test results with field data showed that false positives are common and likely related to experimental variability or toxicity to selected test species without measureable effects on the ecosystem. Results from microcosm studies have consistently demonstrated that chemical exposures exceeding the acute or chronic toxicity concentrations for highly sensitive species may cause little or no ecologically significant damage to an aquatic ecosystem. Sources of uncertainty identified when extrapolating from single species tests to ecological effects were: variability in individual response to pesticide exposure; variation among species in sensitivity to pesticides; effects of time varying and repeated exposures; and extrapolation from individual to population-level endpoints. Data sets from the Chesapeake Bay area (Maryland) were used to show the importance of using “multiple lines of evidence” when assessing biological impact due to conflicting results reported from ambient water column and sediment toxicity tests and biological indices (benthic and fish IBIs). Results from water column and sediment toxicity tests with multiple species in tidal areas showed that no single species was consistently the most sensitive. There was also a high degree of disagreement between benthic and fish IBI data for the various stations. The lack of agreement for these biological community indices is not surprising due to the differences in exposure among habitats occupied by these different taxonomic assemblages. Data from a fish IBI, benthic IBI and Maryland Physical Habitat Index (MPHI) were compared for approximately 1100 first through third-order Maryland non-tidal streams to show the complexity of data interpretation and the incidence of conflicting lines of evidence. A key finding from this non-tidal data set was the need for using more than one biological indicator to increase the discriminatory power of identifying impaired streams and reduce the possibility of “false negative results”. Based on historical data, temporal variability associated with an IBI in undisturbed areas was reported to be lower than the variability associated with single species toxicity tests.     

Iron overload following red blood cell transfusion and its impact on disease severity

Transfusion of red blood cells can be a life-saving therapy both for patients with chronic anemias and for those who are critically ill with acute blood loss. However, transfusion has been associated with significant morbidity. Chronic transfusion results in accumulation of excess iron that surpasses the binding capacity of the major iron transport protein, transferrin. The resulting non-transferrin bound iron (NTBI) can catalyze the production of highly reactive oxygen species (ROS) leading to significant and wide spread injury to the liver, heart, and endocrine organs as well as increases in infection. Acute transfusion of red blood cells in critically ill patients likewise has significant effects including increased mortality, prolonged hospital stays, and elevated risk of nosocomial infection. These effects appear to be more profound with increasing age of stored blood. The progressive release of free iron associated with storage time suggests that morbidity following acute transfusion, like that seen in chronic transfusion, may be due in part to elevated levels of NTBI. It is clear that transfusion is necessary in many instances; however, its risks and benefits must be carefully balanced before proceeding to avoid unnecessary iron toxicity.     

Toxicity analysis of freshwater and marine sediments with meio- and macrobenthic organisms: a review

Benthic metazoans play a key role as test organisms in toxicity analyses of aquatic ecosystems. This report gives an overview of the species of benthic metazoans used for the assessment of toxicity in freshwater and marine sediments, as well as of the criteria relevant to the choice between test species and procedures. The main applications of these organisms are mono-species bioassays, test-batteries, analyses of benthic communities and bioaccumulation studies. Sediment toxicity assays, including acute and chronic exposures, have been developed for nematodes, insects, oligochaetes, polychaetes, crustaceans, molluscs and echinoderms. At least 30 species of freshwater and 71 species of marine and estuarine benthic metazoans have thus far been used in sediment toxicity bioassays. Although aquatic pollution is a world-wide problem, most sediment toxicity bioassays have been developed for organisms native to Europe and North America. The most common bioassay endpoints are mortality, development, growth and behavioural responses. The value of genetic, biochemical, physiological and pathological responses as toxicity endpoints is currently being investigated. The quest for additional test species and protocols is still a worthwhile endeavour in sediment ecotoxicology.     

Ecotoxicological assessment of water and sediment of the Corumbataí River, SP, Brazil.

The Corumbataí River drains an economically important area which is mainly represented by the municipalities of Piracicaba and Rio Claro. In view of the impacts caused by the discharge of industrial waste and domestic sewage into the Piracicaba River, the Corumbataí has become increasingly significant as a source of water for the municipality of Piracicaba. However, chemical, physical, and microbiological analyses carried out prior to the present study had already indicated a decline in the quality of the Corumbataí waters. This study aimed to assess, through water and sediment samples, both acute and chronic toxicity to Daphnia magna and Daphnia similis, and to analyze acid-volatile sulfide (AVS) and simultaneously extracted metal (SEM) in the sediment. Resulting data were intended to be a contribution to future projects for the management and recuperation of this system. To that aim, water and sediment were collected at seven Corumbataí sampling stations in November 2003 and March 2004. Acute toxicity to D. similis was detected in water and sediment samples from the Piracicaba station, located at the mouth of the Corumbataí River. Chronic toxicity was identified in the water or sediment samples of all stations, with the exception of Analandia Montante (upstream), at the head of the river. This was found to affect survival, growth, and fecundity of the test-organisms. The AVS and SEM analyses showed the bioavailability of the metals, thus explaining toxicity found in bioassaying samples of water and sediment. The use of two test-organism species made it possible to obtain a better assessment of the condition of both water and sediment samples of the Corumbataí River.     

Studies on the use of uncertainty factors in deriving RfDs

Risk assessment of exposure to chemicals having a toxic end point routinely uses the reference dose (RfD) approach based on uncertainty factors of 10. RfD model can be used with widely different databases. However, the quality of individual risk assessment is unequal among chemicals, often resulting in either an over‐ or underestimation of adverse health risk. The purpose of this investigation was to evaluate whether the magnitude of the 10X uncertainty factors has scientific merit against data from recent human and animal experimental studies. Although we assessed the use of uncertainty factors for representative chemicals from various classes of compounds, such as volatile organics, alcohols, gasoline components, and pesticides, we are presenting our findings for 24 chemicals.

A compilation and comparison of ratios between LOAEL/NOAEL (Lowest Observed Adverse Effect Level/No Observed Adverse Effect Level), and subchronic/chronic values were made. Although a 10X uncertainty factor is most commonly used in the risk assessment processes, an examination of the datasets which have been used to calculate RfDs suggests different values which are scientifically justifiable.     

Predictive Value of Species Sensitivity Distributions for Effects of Herbicides in Freshwater Ecosystems

In this article we present a review of the laboratory and field toxicity of herbicides to aquatic ecosystems. Single-species acute toxicity data and (micro)mesocosm data were collated for nine herbicides. These data were used to investigate the importance of test species selection in constructing species sensitivity distributions (SSDs), and in estimating hazardous concentrations (i.e., HC5) protective for freshwater aquatic ecosystems. A lognormal model was fitted to toxicity data (acute EC50s and chronic NOECs) and the resulting distribution used to estimate lower (95% confidence), median (50% confidence), and upper (5% confidence), HC5 values. The taxonomic composition of the species assemblage used to construct the SSD does have a significant influence on the assessment of hazard and only sensitive primary producers should be included for the risk assessment of herbicides. No systematic difference in sensitivity between standard and non-standard test species was observed. Hazardous concentrations estimated using laboratory-derived acute and chronic toxicity data for sensitive freshwater primary producers were compared to the response of herbicide-stressed freshwater ecosystems using a similar exposure regime. The lower limit of the acute HC5 and the median value of the chronic HC5 were protective of adverse effects in aquatic micro/mesocosms even under a long-term exposure regime. The median HC5 estimate based on acute data was protective of adverse ecological effects in freshwater ecosystems when a pulsed or short-term exposure regime was used in the microcosm and mesocosm experiments. There was also concordance between the predictions from the effect model PERPEST and the concentrations at which clear effects started to emerge in laboratory and field studies. However, compared to the SSD concept, the PERPEST model is able to provide more information on ecological risks when a common toxicological mode of action is evaluated as it considers both recovery and indirect effects.     

Extrapolation for Exposure Duration in Oral Toxicity: A Quantitative Analysis of Historical Toxicity Data

For human risk assessment, experimental data often have to be extrapolated for exposure duration, which is generally done by means of default values. The purpose of the present study was twofold. First, to derive a statistical distribution for differences in exposure duration that can be used in a probabilistic concept for combining assessment factors in risk characterization. Second, to obtain insight in the magnitude of the change in No-Observed-Adverse-Effect-Level (NOAEL) with exposure duration, which will lead to more science-based assessment factors for exposure duration. A large historical database, including 198 substances, was consulted. Ratios were calculated for pairs of NOAELs for systemic toxicity from oral toxicity studies with the same species (rats or mice, various strains) and different exposure duration categories. The Geometric Mean (GM), Geometric Standard Deviation (GSD), and the 90th and 95th percentile values were determined. The traditionally applied default factors for subacute to semichronic (10), for semichronic to chronic (10), and for subacute to chronic exposure (100) corresponded with the 93, 87, and 99-percentiles of the respective distributions. Options are presented for a set of default values and probabilistic distributions for assessment factors for exposure duration based on data from the consulted historical database.     

嗜酸乳杆菌LA-G80的毒理学研究

目的对嗜酸乳杆菌的毒性进行研究。方法采用大、小鼠急性毒性试验、Ames试验、小鼠骨髓细胞微核试验、小鼠精子畸形试验和大鼠30 d喂养等对嗜酸乳杆菌进行安全性试验研究。结果急性经口毒性试验表明,大、小鼠灌胃给予嗜酸乳杆菌,最大耐受剂量雌雄两性别均大于20.0 g/kg体重,Ames试验、微核试验和精子畸形试验结果均为阴性。大鼠30 d喂养试验结果表明各项指标均未见明显毒性反应。结论在本次实验条件下,嗜酸乳杆菌未见遗传毒性。由此可初步判定,使用嗜酸乳杆菌是安全可靠的。     

Implementation of a multiple biomonitoring approach to evaluate the potential for impact from an industrial discharge

Over a 2-year period, an industrial discharger implemented a program to determine if there was a potential for in-stream impact from its discharge, and, if necessary, to eliminate that potential. Six basic study designs were used. These included: (1) ambient toxicity tests using indicator organisms; (2) in-stream waste concentration (IWC) chronic testing using indicator organisms; (3) on-site flow-through toxicity testing using indicator and resident species with receiving stream water as the diluent; (4) in situ acute toxicity studies using indicator and resident species; (5) biological surveys of the receiving stream; and (6) artificial stream studies. The outcome of the studies resulted in conclusive data on which to base the design of a diffuser to dilute the effluent 1:20. This concentration was well below the lowest acute no-observed-effect concentration (10% effluent) determined using sensitive resident test species. In this manner, impact from the effluent on the James River had been reduced so that even the most sensitive resident species were protected. As a result of the study, the facility's permit was modified so that toxicity tests were made only on effluent diluted with receiving stream water to represent dilution at 1Q10 rather than 100 percent effluent. Follow-up studies have concentrated on a series of toxicity tests which were designed to identify the toxicants in the final effluent.     

Detecting Heterogeneity of Substitution along DNA and Protein Sequences

Regions of differing constraint, mutation rate or recombination along a sequence of DNA or amino acids lead to a nonuniform distribution of polymorphism within species or fixed differences between species. The power of five tests to reject the null hypothesis of a uniform distribution is studied for four classes of alternate hypothesis. The tests explored are the variance of interval lengths; a modified variance test, which includes covariance between neighboring intervals; the length of the longest interval; the length of the shortest third-order interval; and a composite test. Although there is no uniformly most powerful test over the range of alternate hypotheses tested, the variance and modified variance tests usually have the highest power. Therefore, we recommend that one of these two tests be used to test departure from uniformity in all circumstances. Tables of critical values for the variance and modified variance tests are given. The critical values depend both on the number of events and the number of positions in the sequence. A computer program is available on request that calculates both the critical values for a specified number of events and number of positions as well as the significance level of a given data set.     

稀有鮈鲫对重铬酸钾和3,4-二氯苯胺急性毒性研究

目的和方法稀有鮈鲫(Gobiocypris rarus)作为一种本土特有的小型鱼类,是我国正在标准化的化学品毒性测试生物之一。为评价稀有鮈鲫鱼类急性毒性实验中效应的稳定性和可重复性,研究优化筛选了重铬酸钾和3,4-二氯苯胺两种化学品,分别在单一实验室内及不同实验室间进行急性毒性验证实验。结果对于来源相同、体长固定的稀有鮈鲫,无论在实验室内还是实验室间,两组化学品的96 h LC50值均在x珋±2s的质量控制范围之内,所有结果体现了很好的稳定性和可重复性。结论根据研究获得的数据可建立一个有效的稳定性和可重复性衡量数据库,用来评估之后其他单个实验的可靠性;稀有鮈鲫作为一种具有潜力的生态毒性测试的生物种类,具有成为标准实验动物的潜能。     

Effects of ammonia on monoamine oxidase and enzymes of GABA metabolism in mouse brain.

Acute and chronic ammonia toxicity was produced in the mice by intraperitoneal injection of ammonium chloride (200 mg/kg) and by exposure of mice to ammonia vapours (5% v/v) continuously for 2 days and 5 days respectively. The ammonia content was elevated in the cerebellum, cerebral cortex and brain stem and in liver. In acute ammonia intoxication there was a decrease in the monoamine oxidase (MAO) activity in all the three regions of brain. In chronic ammonia toxicity (2 days of exposure) a significant increase in the activity of MAO was observed in the cerebral cortex while in cerebellum and brain stem there was a significant decrease. In cerebral cortex and cerebellum there was a rise in the activity of MAO as a result of exposure to ammonia vapours for 5 days. A significant decrease was observed in the activity of glutamate decarboxylase (GAD) in all the three regions of the brain both in acute and chronic ammonia toxicity (2 days). There was a decrease in the activity of this enzyme only in the cerebral cortex in the animals exposed to ammonia for 5 days. The activity of GABA-aminotransferase (GABA-T) showed a significant rise in cerebellum and a fall in the brain stem in acute ammonia toxicity. In chronic ammonia toxicity GABA-T showed a rise in all the three regions of brain. Chronic ammonia toxicity produced a significant decrease in the content of glutamate in all the three regions without a significant change in the content of aspartate. GABA and glutamine. The content of alanine increased in all the three regions of brain under these experimental conditions. The ratio of glutamate + aspartate/GABA and glutamate/glutamine showed a decrease in all the three regions as a result of ammonia toxicity.