Saturation units for use in aquatic bioassays.

Methods were developed for preparing liquid/liquid and glass wool column saturators for generating chemical stock solutions for conducting aquatic bioassays. Exposures have been conducted using several species of fish, invertebrate, and mollusks in static and flow-through conditions using these methods. Stock solutions for 82 organic chemicals were prepared using these saturation units. The primary purpose of stock generation was to provide a continuous and consistent amount of toxicant laden solution at a measured analytical level which would be available to test organisms for the test duration. In the present study, the glass wool column and liquid/liquid saturators were used to provide consistent stock concentrations, at times approaching saturation, for fathead minnow (Pimephales promelas) acute exposures. Attempts were made to achieve the maximum solubility of these compounds for comparison purposes to water solubility values available in the literature. Literature solubility values from a database by Yalkowsky et al. [1] provided information on temperatures and data quality which allowed comparison to values obtained from the present study. Twenty four compounds were identified and analyzed for the comparison of maximum obtainable solubility levels. Maximum saturator stock water concentrations were generally lower (R = 0.98) but were in close agreement with published water solubility values.

Use of knowledge bases and QSARs to estimate the relative ecological risk of agrichemicals: a problem formulation exercise.

Ecological risk assessments can be used to establish the likelihood that an adverse effect will result from exposure to one or more chemicals. When evaluating contaminated sites with many chemicals present, risk assessors must grapple with the problem of quickly identifying the chemicals that are most likely to be of concern, based on effect and exposure assessment information. Many times data gaps exist and the risk assessor is left with decisions on which models to use to estimate the parameter of concern. In the present paper, a procedure is presented for ranking agrichemicals, utilizing the ASTER (ASsessment Tools for the Evaluation of Risk) system. The procedure was employed to rank the relative ecological risk of forty-nine pesticides historically used in agricultural sites in the Walnut Creek watershed near Ames, lowa, USA. Empirical data from the ASTER system were used when available in the associated databases, and quantitative structure-activity relationships and expert systems were invoked when data were lacking. Separate rankings were conducted based on major species taxonomic groupings. Resulting toxic effects thresholds were compared to surface water concentrations.

A QSAR study of the toxicity of amines to the fathead minnow.

Simple and multiple linear regressions were applied to the development of fish toxicity QSAR models for the 96-h LC50 to the fathead minnow, Pimephales promelas. The data on unbranched saturated primary alkylamines as well as the complete data set were well-fitted to linear QSAR models using log P or the valence first-order connectivity index (1XV) as descriptors. Although adding data on other subclasses of amines in this data set yield acceptable QSARs, only the tertiary amine subclass provided a poor fit with both of these descriptors. The amines include both acyclic and cyclic derivatives, either with no additional functional groups, or with the hydroxyl, keto, methoxy, and propargyl moieties. The molecular mechanism for fish toxicity of these amines as well as the outliers in the study were investigated. Based upon the calculated log P value of -1.40, tripropargylamine has an apparent excess toxicity of 84 times; in contrast, the measured shake-flask log P for this compound was subsequently found to be 1.26, giving a predicted LC50 consistent with the observed value. An upward curvature of the QSAR plot for the most hydrophilic compounds suggests a shift in mechanism for the lowest members of the series.

ASTER: an integration of the AQUIRE data base and the QSAR system for use in ecological risk assessments.

Ecological risk assessments are used by the US Environmental Protection Agency (US EPA) and other governmental agencies to assist in determining the probability and magnitude of deleterious effects of hazardous chemicals on plants and animals. These assessments are important steps in formulating regulatory decisions. The completion of an ecological risk assessment requires the gathering of ecotoxicological hazard and environmental exposure information. This information is evaluated in the risk characterization section to assist in making the final risk assessment. ASTER (ASsessment Tools for the Evaluation of Risk) was designed by the US EPA Environmental Research Laboratory-Duluth (ERL-D) to assist regulators in producing assessments. ASTER is an integration of the ACQUIRE (AQUatic toxicity Information REtrieval system) and QSAR (Quantitative Structure Activity Relationships) systems. ACQUIRE is a data base of aquatic toxicity tests and QSAR is comprised of a data base of measured physicochemical properties, and various QSAR models that estimate physicochemical and ecotoxicological endpoints. ASTER will be available to international governmental agencies through the US EPA National Computing Center.

QSAR modelling of the ERL-D fathead minnow acute toxicity database.

1. Regression analysis has been applied to examine the structure-activity relationships regarding the acute fish toxicity (96 h LC50 fathead minnow) of organic chemicals. The log P dependent baseline toxicity model has been confirmed for a data set composed of 618 compounds from 24 chemical classes associated with a putative common mode of action. 2. Covariance analysis of the discrete by class regression functions resulted in the combination of chemicals to subsets associated with their mode of action. Separate models were derived for nonpolar (Class I) and polar (Class II and III) compounds. Chemicals which are more toxic than estimated from the baseline model are identified.

The toxicity of acetylenic alcohols to the fathead minnow, Pimephales promelas: narcosis and proelectrophile activation.

1. The 96-h LC50 values for 16 acetylenic alcohols in the fathead minnow (Pimephales promelas) were determined using continuous-flow diluters. The measured LC50 values for seven tertiary propargylic alcohols agreed closely with the QSAR predictions based upon data for other organic non-electrolytes acting by a narcosis mechanism. 2. Four primary and four secondary propargylic alcohols were 7 to 4600 times more toxic than the respective narcotic toxicity estimated by QSAR. Metabolic activation to electrophilic alpha,beta-unsaturated propargylic aldehydes or ketones is proposed to account for the increased toxicity. 3. 3-Butyn-1-ol and 4-pentyn-2-ol, primary and secondary homopropargylic alcohols, were 320 and 160, respectively, times more toxic than predicted. In this case an activation step involving biotransformation to an allenic electrophile intermediate was proposed.