Test Endpoints Research Articles

Within-tester repeatability and between-tester reproducibility of skin test endpoint titration: A quality assurance study

Within-tester repeatability and between-tester reproducibility of skin test endpoint titration: A quality assurance study

Safety Pharmacology Study Results and their Impact on the Design of First-in-human Trials for Authorised Oncology Therapies

Safety pharmacology studies are conducted to elucidate possible safety risks on cardiovascular (CV), central nervous system (CNS) and respiratory systems, and are usually carried out prior to first-in-human (FIH) trials. These tests are either standalone tests, or have relevant endpoints integrated in repeat-dose toxicology studies. To review safety pharmacology study results for authorised oncology therapies and to assess how these results have impacted the design of FIH trials of these agents. Bearing in mind the 3Rs principle for animal use (reduction, refinement and replacement), the design of safety pharmacology studies and their outcome for 30 new anticancer medicinal products (both small molecules and biotechnology-derived products) authorised by the European Medicines Agency (EMA) between 2011 and 2015 was reviewed. The impact of the safety pharmacology study results on the design of the FIH trials was also investigated. Our analysis shows that all CNS and respiratory safety pharmacology tests were negative, while for the CV system, 61% of small molecules had positive effects in vitro and/or in vivo and only one out of seven biotechnology-derived products had positive effects in vivo. Regarding the impact of safety pharmacology on clinical trial study design, CV safety pharmacology results for small molecules influenced FIH trial designs in 60% of cases. Based on this subset of data in the oncology therapeutic area, results indicate that the use of safety pharmacology endpoints in repeat-dose toxicology tests could be further utilised as compared with stand-alone safety pharmacology studies, in particular for the CNS and respiratory systems.

Development of cardiovascular and neurodevelopmental metrics as sublethal endpoints for the Fish embryo toxicity test.

The fathead minnow fish embryo toxicity (FET) test has been proposed as a more humane alternative to current toxicity testing methods as younger organisms are thought to experience less distress during toxicant exposure. However, the FET test protocol does not include endpoints that allow for the prediction of sublethal adverse outcomes, limiting its utility relative to other test types. Researchers have proposed the development of sublethal endpoints for the FET test to increase its utility. The present study 1) developed methods for previously unmeasured sublethal metrics in fathead minnows (i.e., spontaneous contraction frequency and heart rate) and 2) investigated the responsiveness of several sublethal endpoints related to growth (wet wt, length, and growth-related gene expression), neurodevelopment (spontaneous contraction frequency, eye size, and neurodevelopmental gene expression), and cardiovascular function and development (pericardial area, heart rate, and cardiovascular system-related gene expression) as additional FET test metrics using the model toxicant 3,4-dichloroaniline. Of the growth, neurological, and cardiovascular endpoints measured, length, eye size, and pericardial area were found to be more responsive than the other endpoints evaluated. Future studies linking alterations in these endpoints to longer-term adverse impacts are needed to fully evaluate the predictive power of these metrics in chemical and whole-effluent toxicity testing. Environ Toxicol Chem 2018;37:2530-2541. © 2018 SETAC.

Predictive models for acute oral systemic toxicity: A workshop to bridge the gap from research to regulation

In early 2018, the Interagency Coordinating Committee for the Validation of Alternative Methods (ICCVAM) published the “Strategic Roadmap for Establishing New Approaches to Evaluate the Safety of Chemicals and Medical Products in the United States” [1]. Cross-agency federal workgroups have been established to implement this roadmap for various toxicological testing endpoints, with an initial focus on acute toxicity testing. The ICCVAM acute toxicity workgroup (ATWG) helped organize a global collaboration to build predictive in silico models for acute oral systemic toxicity, based on a large dataset of rodent studies and targeted towards regulatory needs identified across federal agencies. Thirty-two international groups across government, industry, and academia participated in the project, culminating in a workshop in April 2018 held at the National Institutes of Health (NIH). At the workshop, computational modelers and regulatory decision makers met to discuss the feasibility of using predictive model outputs for regulatory use in lieu of acute oral systemic toxicity testing. The models were combined to yield consensus predictions which demonstrated excellent performance when compared to the animal data, and workshop outcomes and follow-up activities to make these tools available and put them into practice are discussed here.

Investigation of clearance rate as an endpoint in toxicity testing with freshwater mussels (Unionidae)

The implementation of ecologically relevant sub-lethal endpoints in toxicity testing with freshwater mussels can provide valuable information during risk assessment, especially since these organisms are often exposed to low levels of contaminants. This study examined how to optimize quantifying the filtering capacity or clearance rate (CR) of mussels after exposure to a reference toxicant, sodium chloride (NaCl). CR was defined as the number of algal cells an individual mussel can remove from the overlying water by filtration over time and was determined using spectrophotometric absorbance and direct microscopic examination. Optimization included consideration of the following factors: concentration of algae mixture at test initiation, duration of CR assay, and statistical power. Experimental vessels contained either juvenile (ten, ~ 4 months old) or adult (one, ~ 2.5 years old) Lampsilis siliquoidea. To detect a 10% change in filtering capacity, the optimized adult CR assay was run for 48 h with 2.7 × 107 cells/mL of algae added at test initiation and a minimum of 6 replicates per treatment. The optimized juvenile mussel CR assay was run for 48 h with 1.77 × 107 cells/mL of algae added at test initiation; however, 13 replicates would be required to detect a 10% change to satisfy each method. To reduce the number of juvenile mussels used in testing, a minimum of 4 replicates per treatment was recommended to detect a 25% change in CR. After exposure to a reference toxicant (NaCl), EC50s from the optimized CR assay were compared to two other mussel toxicity endpoints: survival and burial (ability of mussels to bury in clean sand). CR by direct microscopic examination was slightly more sensitive than survival and burial in juveniles and only slightly more sensitive than survival in adults. No significant differences (p > 0.05) were detected between the EC/LC50 values determined from CR and the less labour-intensive survival and burial endpoints. The present study suggests the CR for juvenile and adult L. siliquoidea remained largely unaffected in mussels that survived a 7-day NaCl exposure.

Hybrid in silico/in vitro target fishing to assign function to “orphan” compounds of food origin – The case of the fungal metabolite atromentin

Many small molecules of food origin may effect human health but lack an adequate description of their biological activity. To fill this knowledge gap, a first-line workflow is needed to assign putative functions, rank the endpoints for testing and guide wet-lab experiments. In this framework, the identification of potential biological targets can be used to probe the activity of orphan compounds using a so-called “target fishing” approach. Here, we present a proof of concept study using an in silico/in vitro target fishing approach on the fungal secondary metabolite atromentin. The procedure relies on a computational screening for activity identification coupled with experimental trials for dose-response characterization. Computational results identified estrogen receptors and 17-β-hydroxysteroid dehydrogenase as potential targets. Experiments confirmed a weak estrogenic activity, supporting the reliability of the procedure. Despite limited estrogenicity of atromentin, the proposed inhibition of 17-β-hydroxysteroid dehydrogenase should be considered as a source for endocrine disruptive effects.

Prevalidation of an Acute Inhalation Toxicity Test Using the EpiAirwayIn VitroHuman Airway Model

Introduction: Knowledge of acute inhalation toxicity potential is important for establishing safe use of chemicals and consumer products. Inhalation toxicity testing and classification procedures currently accepted within worldwide government regulatory systems rely primarily on tests conducted in animals. The goal of the current work was to develop and prevalidate a nonanimal (in vitro) test for determining acute inhalation toxicity using the EpiAirway™ in vitro human airway model as a potential alternative for currently accepted animal tests.Materials and Methods: The in vitro test method exposes EpiAirway tissues to test chemicals for 3 hours, followed by measurement of tissue viability as the test endpoint. Fifty-nine chemicals covering a broad range of toxicity classes, chemical structures, and physical properties were evaluated. The in vitro toxicity data were utilized to establish a prediction model to classify the chemicals into categories corresponding to the currently accepted Globally Harmonized System (GHS) and the Environmental Protection Agency (EPA) system.Results: The EpiAirway prediction model identified in vivo rat-based GHS Acute Inhalation Toxicity Category 1–2 and EPA Acute Inhalation Toxicity Category I–II chemicals with 100% sensitivity and specificity of 43.1% and 50.0%, for GHS and EPA acute inhalation toxicity systems, respectively. The sensitivity and specificity of the EpiAirway prediction model for identifying GHS specific target organ toxicity-single exposure (STOT-SE) Category 1 human toxicants were 75.0% and 56.5%, respectively. Corrosivity and electrophilic and oxidative reactivity appear to be the predominant mechanisms of toxicity for the most highly toxic chemicals.Conclusions: These results indicate that the EpiAirway test is a promising alternative to the currently accepted animal tests for acute inhalation toxicity.

Sand Goby—An Ecologically Relevant Species for Behavioural Ecotoxicology

Locomotion-based behavioural endpoints have been suggested as suitable sublethal endpoints for human and environmental hazard assessment, as well as for biomonitoring applications. Larval stages of the sand goby (Pomatoschistus minutus) possess a number of attractive qualities for experimental testing that make it a promising species in behavioural ecotoxicology. Here, we present a study aimed at developing a toolkit for using the sand goby as novel species for ecotoxicological studies and using locomotion as an alternative endpoint in toxicity testing. Exposure to three contaminants (copper (Cu), di-butyl phthalate (DBP) and perfluorooctanoic acid (PFOA) was tested in the early life stages of the sand goby and the locomotion patterns of the larvae were quantified using an automatic tracking system. In a photo-motor test, sand goby larvae displayed substantially higher activity in light than in dark cycles. Furthermore, all tested compounds exerted behavioural alterations, such as hypo- and hyperactivity. Our experimental results show that sand goby larvae produce robust and quantifiable locomotive responses, which could be used within an ecotoxicological context for assessing the behavioural toxicity of environmental pollutants, with particular relevance in the Nordic region. This study thus suggests that sand goby larvae have potential as an environmentally relevant species for behavioural ecotoxicology, and as such offer an alternative to standard model species.

Enhancing the fathead minnow fish embryo toxicity test: Optimizing embryo production and assessing the utility of additional test endpoints

The fathead minnow fish embryo toxicity (FET) test has been identified as a potential alternative to toxicity test methods that utilize older fish. However, several challenges have been identified with the fathead minnow FET test, including: 1) difficulties in obtaining appropriately-staged embryos for FET test initiation, 2) a paucity of data comparing fathead minnow FET test performance to the fathead minnow larval growth and survival (LGS) test and 3) a lack of sublethal endpoints that could be used to estimate chronic toxicity and/or predict adverse effects. These challenges were addressed through three study objectives. The first objective was to optimize embryo production by assessing the effect of breeding group composition (number of males and females) on egg production. Results showed that groups containing one male and four females produced the largest clutches, enhancing the likelihood of procuring sufficient numbers of embryos for FET test initiation. The second study objective was to compare the performance of the FET test to that of the fathead minnow LGS test using three reference toxicants. The FET and LGS tests were similar in their ability to predict the acute toxicity of sodium chloride and ethanol, but the FET test was found to be more sensitive than the LGS test for sodium dodecyl sulfate. The last objective of the study was to evaluate the utility and practicality of several sublethal metrics (i.e., growth, developmental abnormalities and growth- and stress-related gene expression) as FET test endpoints. Developmental abnormalities, including pericardial edema and hatch success, were found to offer the most promise as additional FET test endpoints, given their responsiveness, potential for predicting adverse effects, ease of assessment and low cost of measurement.

Effects of temperature, genetic variation and species competition on the sensitivity of algae populations to the antibiotic enrofloxacin

Primary producers are amongst the most sensitive organisms to antibiotic pollution in aquatic ecosystems. To date, there is little information on how different environmental conditions may affect their sensitivity to antibiotics. In this study we assessed how temperature, genetic variation and species competition may affect the sensitivity of the cyanobacterium Microcystis aeruginosa and the green-algae Scenedesmus obliquus to the antibiotic enrofloxacin. First, we performed single-species tests to assess the toxicity of enrofloxacin under different temperature conditions (20°C and 30°C) and to assess the sensitivity of different species strains using a standard temperature (20°C). Next, we investigated how enrofloxacin contamination may affect the competition between M. aeruginosa and S. obliquus. A competition experiment was performed following a full factorial design with different competition treatments, defined as density ratios (i.e. initial bio-volume of 25/75%, 10/90% and 1/99% of S. obliquus/M. aeruginosa, respectively), one 100% S. obliquus treatment and one 100% M. aeruginosa treatment, and four different enrofloxacin concentrations (i.e. control, 0.01, 0.05 and 0.10mg/L). Growth inhibition based on cell number, bio-volume, chlorophyll-a concentration as well as photosynthetic activity were used as evaluation endpoints in the single-species tests, while growth inhibition based on measured chlorophyll-a was primarily used in the competition experiment. M. aeruginosa photosynthetic activity was found to be the most sensitive endpoint to enrofloxacin (EC50–72h =0.02mg/L), followed by growth inhibition based on cell number. S. obliquus was found to be slightly more sensitive at 20°C than at 30°C (EC50–72h cell number growth inhibition of 38 and 41mg/L, respectively), whereas an opposite trend was observed for M. aeruginosa (0.047 and 0.037mg/L, respectively). Differences in EC50–72h values between algal strains of the same species were within a factor of two. The competition experiment showed that M. aeruginosa growth can be significantly reduced in the presence of S. obliquus at a density ratio of 75/25% M. aeruginosa/S. obliquus, showing a higher susceptibility to enrofloxacin than in the single-species test. The results of this study confirm the high sensitivity of cyanobacteria to antibiotics and show that temperature and inter-strain genetic variation may have a limited influence on their response to them. The results of the competition experiment suggest that the structure of primary producer communities can be affected, at least temporarily, at antibiotic concentrations close to those that have been measured in the environment.

Burrowing behavior of Chironomus yoshimatsui larvae as an indicator of freshwater quality

A new behavioral endpoint in ecotoxicity testing, burrowing behavior of Chironomus yoshimatsui larvae that survived pre-exposure to 0, 1, 5, and 10mg/L of cadmium for 96h was evaluated in a system composed of clean reconstituted water and sand for 5h, at 30min intervals. The effective time required for 50% of the introduced larvae to burrow (ET50), the proportion of the maximum burrowing rate reached during a 5h period (BR5h), and the area under the curve at 5h (AUC5h) were calculated based on the fitted relationship between burrowing rate and elapsed time. These effect parameters were chosen because they take into account either the burrowing speed of the larvae (ET50), or the proportion of the maximum burrowing rate reached during a 5h period (BR5h), or both (AUC5h). We found that higher cadmium concentrations resulted in longer ET50 and lower AUC5h values. Additionally, field water samples were collected from streams near residential, natural, agricultural, and industrial areas in Ansan City, Korea in 2014 and 2015, and were used to validate the proposed burrowing test method. The results of the burrowing tests with field collected water samples also confirmed the sensitivity of burrowing activity as an ecotoxicity endpoint, indicated by the large differences among the ET50, BR5h, and AUC5h across the sampling sites and dates with industrial sites strongly affecting burrowing behavior. This study clearly showed that the proposed burrowing test could provide information that would not be detected with the existing acute toxicity tests, within a relatively short time, and can therefore be used as a complement to existing chemical analyses and acute toxicity tests.

What do we know about the ecotoxicology of pharmaceutical and personal care product mixtures? A critical review

ABSTRACTNo uniform regulation for risk assessment of pharmaceutical and personal care products (PPCP) mixtures is currently available. Hence, a large diversity of strategies can be used for studying cocktail effects of PPCP, which makes difficult the task of incorporating this challenging issue into regulatory frameworks. This review provides an updated state of knowledge on the ecotoxicity of PPCP mixtures, including 194 assessments of the toxicity of mixtures from 65 articles published during 2000–2017. The misunderstandings, deficiencies and data gaps identified from those studies were critically discussed based on the models/tools used to predict/assess the joint effects and the interpretation and presentation of the effect profiles, the experimental designs used, the qualitative and quantitative composition of the PPCP mixtures and the type of bioassays performed regarding test duration, endpoints and levels of biological organization. Possible approaches pointed out in the literature to deal with the identified critical issues were also discussed. Overall, we have identified that further advances in this field of research still lack robust and consistent studies regarding the experimental design and the approaches and terminologies used to calculate, interpret and report the joint effects.

Toxicity estimates for diuron and atrazine for the tropical marine cnidarian Exaiptasia pallida and in-hospite Symbiodinium spp. using PAM chlorophyll-a fluorometry

Effective ecotoxicological risk assessments for herbicides in tropical marine environments are restricted by a lack of toxicity data, sensitive test methods and endpoints for relevant species, and this requires rectification. The symbiotic sea anemone Exaiptasia pallida is a suitable test species, representing the phylum Cnidaria and allowing for assessments of toxicological responses of both the animal host and in-hospite Symbiodinium spp. Pulse amplitude modulated (PAM) chlorophyll-a fluorometry is recognised as a valuable ecotoxicological tool, and here newly-developed test methods are presented using PAM fluorometry to measure herbicide effects on photosynthetic efficiency of in-hospite Symbiodinium spp. Additionally, measurements on healthy laboratory-reared E. pallida provide baseline data demonstrating the normal effective quantum yield (EQY) and the maximum electron transport rate (ETRm) for Symbiodinium spp. in the absence of herbicide stress. Concentration-dependant reductions in the EQY and ETRm occurred during diuron and atrazine exposures; a mean 48-h EC50 (effective concentration; 50%) of 8μg/L of diuron was estimated, however atrazine elicited a much lower toxicity. Twelve-day exposures to 10–200μg/L diuron showed that the greatest EQY effect occurred during the first 48h, with little subsequent change. However, longer exposures to the lowest diuron treatment (1μg/L) showed the lowest EQYs after 96h followed by recovery to control levels within 12d. Furthermore, asexual reproduction was inhibited during 12-d exposures to diuron, and 12-d EC50 values of 100 and 132μg/L were estimated to inhibit successful reproduction of pedal lacerates and juveniles by 50% respectively. This study provides much needed data contributions to species sensitivity curves for development of diuron and atrazine water quality guidelines in tropical marine environments.

The effect of prior knowledge of test endpoint on non-local muscle fatigue.

If the work duration or volume is known, it is common for individuals to anticipate this challenge by pursuing a strategy that may decrease the initial force output and maintain a force level that ensures a force reserve towards the end of the task. However, it is unknown whether this is a global strategy that is transferred to a non-exercised muscle following fatigue of a contralateral homologous muscle. To clarify if prior knowledge of task endpoint has an effect on non-local muscle fatigue (NLMF), 15 male participants (22.4 ± 3.8years) completed four conditions: (1) KNtest > fatigue (known endpoint after fatigue), (2) UNKtest > fatigue (unknown endpoint after fatigue), (3) KNtest > control (known endpoint without fatigue), (4) UNKtest > control (unknown endpoint without fatigue). For fatigue conditions, a maximal intensity, unilateral knee extension protocol was completed (two sets of 100s maximal voluntary isometric contractions (MVIC) with 60s rest between), whereas the control condition involved rest (260s). The participants were either informed (known (KN) conditions) or not informed (unknown (UNK) conditions) of the duration of a post-intervention strength-endurance test (contralateral knee extension MVIC, ≥30s). During the strength-endurance test, the UNKtest > fatigue displayed meaningful decreases in force (UNKtest > fatigue 10-12% over first 30s), which was largest at the 25-30-s period (UNKtest > fatigue 7.4-41.1% from 25 to 1930s) compared to KNtest > fatigue and KNtest > control conditions, respectively. Prior knowledge of task endpoint can modify NLMF and affect pacing strategies.

Trajectory of the MAPT-PACC-Preclinical Alzheimer Cognitive Composite in the Placebo Group of a Randomized Control Trial: Results from the MAPT Study: Lessons for Further Trials.

Defining the primary cognitive endpoint is a major decision for Alzheimer's disease preventive trials. As an example for further trials we present in detail the three-year cognitive decline in the placebo group of MAPT trial, a randomized controlled trial (RCT) using a cognitive composite score (MAPT-PACC). Participants were dementia-free adults 70 years or older, with subjective memory complaints. Our findings as expected showed subjects with older age (>75), higher beta amyloid brain deposition, APOE-ε4 allele carriers, with low RBC DHA+EPA levels and higher CDR level are at higher risk of cognitive decline. The data presented in this paper can be useful for future preventive trials to choose the primary cognitive end point, assess the clinical relevance of cognitive changes and perform sample size calculation for several targeted population eg. ApoE4, amyloid +, oldest old, lower n3-PUFA. We believe that the trial group with CDR 0.5, without being selected by a memory test endpoint is a good target population for AD preventive trials.

Evaluating the zebrafish embryo toxicity test for pesticide hazard screening.

Given the numerous chemicals used in society, it is critical to develop tools for accurate and efficient evaluation of potential risks to human and ecological receptors. Fish embryo acute toxicity tests are 1 tool that has been shown to be highly predictive of standard, more resource-intensive, juvenile fish acute toxicity tests. However, there is also evidence that fish embryos are less sensitive than juvenile fish for certain types of chemicals, including neurotoxicants. The utility of fish embryos for pesticide hazard assessment was investigated by comparing published zebrafish embryo toxicity data from pesticides with median lethal concentration 50% (LC50) data for juveniles of 3 commonly tested fish species: rainbow trout, bluegill sunfish, and sheepshead minnow. A poor, albeit significant, relationship (r2 = 0.28; p < 0.05) was found between zebrafish embryo and juvenile fish toxicity when pesticides were considered as a single group, but a much better relationship (r2 = 0.64; p < 0.05) when pesticide mode of action was factored into an analysis of covariance. This discrepancy is partly explained by the large number of neurotoxic pesticides in the dataset, supporting previous findings that commonly used fish embryo toxicity test endpoints are particularly insensitive to neurotoxicants. These results indicate that it is still premature to replace juvenile fish toxicity tests with embryo-based tests such as the Organisation for Economic Co-operation and Development Fish Embryo Acute Toxicity Test for routine pesticide hazard assessment, although embryo testing could be used with other screening tools for testing prioritization. Environ Toxicol Chem 2017;36:1221-1226. © 2016 SETAC.

The Effects of Elevated Specific Conductivity on the Chronic Toxicity of Mining Influenced Streams Using Ceriodaphnia dubia.

Salinization of freshwater ecosystems as a result of human activities has markedly increased in recent years. Much attention is currently directed at evaluating the effects of increased salinity on freshwater biota. In the Central Appalachian region of the eastern United States, specific conductance from alkaline discharges associated with mountain top mining practices has been implicated in macroinvertebrate community declines in streams receiving coal mining discharges. Whole effluent toxicity testing of receiving stream water was used to test the hypothesis that mine discharges are toxic to laboratory test organisms and further, that toxicity is related to ionic concentrations as indicated by conductivity. Chronic toxicity testing using Ceriodaphnia dubia was conducted by contract laboratories at 72 sites with a total of 129 tests over a 3.5 year period. The database was evaluated to determine the ionic composition of mine effluent dominated streams and whether discharge constituents were related to toxicity in C. dubia. As expected, sulfate was found to be the dominant anion in streams receiving mining discharges with bicarbonate variable and sometimes a substantial component of the dissolved solids. Overall, the temporal variability in conductance was low at each site which would indicate fairly stable water quality conditions. Results of the toxicity tests show no relationship between conductance and survival of C. dubia in the mining influenced streams with the traditional toxicity test endpoints. However, consideration of the entire dataset revealed a significant inverse relationship between conductivity and neonate production. While conductivity explained very little of the high variability in the offspring production (r2 = 0.1304), the average numbers of offspring were consistently less than 20 neonates at the highest conductivities.

Institutes in the Lead: Identifying Environmental Factors in Breast Cancer.

Institutes in the Lead: Identifying Environmental Factors in Breast Cancer.

Population dynamics of Parhyale hawaiensis (Dana, 1853) (Amphipoda: Hyalidae) associated with an intertidal algal belt in southeastern Brazil

Static life tables were used to establish demographic parameters such as size-class structure, abundance trends, sex ratio, net reproductive rate, generation time, and per capita rate of population growth for a population of the amphipod Parahyale hawaiensis (Dana, 1853) (Hyalidae) from the intertidal belt of a red alga Bryocladia trysigera (J. Agardh) F. Schmitz in southeastern Brazil. Collections were taken monthly from December 2012 to November 2013. There were two reproductive peaks, a higher one, May to July, and a second throughout the warmer months, October to January. The continuous reproduction results in the overlapping of generations. A sex ratio biased in favor of females was recorded in all sampling dates, a common pattern in epifaunal species. The estimated net reproductive rate was 1.45 ± 1.01 young per female, the generation time 3.51 ± 1.31 months, and the population growth rate 0.06 ± 0.17 per capita per month. The logistic growth model indicates that an initial population of 10 individuals would reach the carrying capacity for the species in a natural environment in 35 to 40 generations time, a period equivalent to 130 to 150 months. As a result of extinction model application, no possibility of extinction was predicted for the local population. The estimated parameters can be used as endpoints in ecotoxicological tests.

Application of root growth endpoint in toxicity tests with lettuce (Lactuca sativa)

Ecotoxicological tests are an important tool to assess the toxicity of chemical substances and even the deleterious effects of adverse environmental conditions to different species. Ecotoxicological studies with land plants and animals are relatively recent compared to those with aquatic species, with few studies reported focusing on terrestrial species. The aim of the present study was to evaluate the sensitivity of root growth (Total Part; Radicle, Hypocotyl) in lettuce (Lactuca sativa) to sodium chloride (NaCl), by means of exposing the seeds to concentrations of 0, 1.0, 2.0, 4.0, 8.0 and 16.0 g L-1 for five days in Petri dishes. The average effective concentration (EC50;120h) on germination was 5.73 ± 0.56 g L-1 (CI= 4.61 to 6.86 g L-1). The effects on root growth were detected starting at a concentration of 1.0 g L-1 of NaCl and the radicle (Rad) was the most sensitive and reliable structure. Root growth was a more sensitive endpoint than germination, since the effects were detected at concentrations some 10 times lower. Besides this, the use of the radicle as an endpoint, proposed in the present study, should be intensified in ecotoxicological studies, since it provides satisfactory results at low cost and in a relatively short time frame.