The environmental fate of phthalate esters: A literature review

A principal goal of pesticide science is to be able to predict the environmental impact of a pesticide before it is released into the environment. To save expense and time, we would like to be able to make such a prediction for each pesticide with as few laboratory experiments on the pesticide as possible, and even fewer field experiments. Environmental processes, however, are enormously complex and sometimes (apparently) random. The sites of most interest—agricultural fields, forests, lakes, streams, etc.—are subtle living ecosystems which are incompletely understood and subject to great variability in space and time. The very diversity and intricacy which are indicators of the health of such ecosystems makes even the definition of what constitutes a significant impact on such systems a difficult task.

The SCS/ARS/CES pesticide properties database for environmental decision-making.

Arctic contaminants : sources, occurrence and pathways

Polycyclic aromatic hydrocarbons (PAHs) appear in most urbanized coastal areas of the world, accumulating in sediments and biota that are unable to efficiently eliminate them. This review focuses specifically on the mechanisms of bioavailability, uptake, and elimination, which determine the extent of accumulation and retention of PAHs in invertebrates and fish in marine ecosystems. We review here the literature on the mechanisms and factors that control these processes which ultimately determine the concentration of PAHs in marine organisms. Understanding both the temporal and spatial characteristics of bioaccumulation of the environmentally important PAHs is crucial for determining the impact that this class of compounds may have on marine populations. To provide a complete assessment of these potential impacts, scientists require knowledge about the distribution of these compounds in different environmental matrices, their uptake and partitioning in different tissues, their rates of elimination, and their potential for persistence in certain species. The combined information on these mechanisms and the environmental factors that control accumulation will help scientists develop predictive models of contaminant accumulation both for acute events, such as oil spills, and for long-term, chronic exposure as is found in many urban areas in our coastal ecosystems.

Bioaccumulation of Polycyclic Aromatic Hydrocarbons by Marine Organisms

European Union Risk Assessment Report

The value of hexavalent chromium as a reference toxicant was investigated by comparing the precision of two laboratories in preparing test solutions, examining the consistency of chromium exposure in the test chambers during experiments and determining the effect of nominal versus measured test concentrations on the calculated toxicity (EC50 or LC50). The sensitivities of the test animals to chromium were also determined.

The coefficients of variation associated with preparing chromium test concentrations were 51 and 63.8% in salt and fresh water, respectively, at one laboratory, and 136 and 14.8%, respectively, at the other laboratory. Hexavalent chromium remained stable in the hexavalent (as prepared) form during the toxicity test, with recoveries ranging from 77 to 114%. The precision of the analytical laboratory in measuring chromium-spiked fresh and salt waters ranged from 0.2 to 9.1%. The impact on the calculated EC50s or LC50s of using analytically measured versus nominal concentrations in the analyses was negligible. A comparison of seven species in 27 tests showed organism sensitivity (mean EC50 or LC50 as mg/L Cr6+) to chromium to be, in decreasing order of sensitivity: Ceriodaphnia sp. (0.031), Daphnia pulex (0.086), Mysidopsis almyra (5.1), Mysidopsis bahia (6.03), Cyprinodon variegatus (21.4), Pimephales promelas (26.1) and Lepomis macrochirus (182.9).

The 48-h LC50s for M. bahia were not significantly different (p < 0.05) either within or between laboratories during a 3-week study; values ranged from 5.49 to 7.72 mg/L Cr6+ in both laboratories (nominally) and from 4.21 to 7.23 mg/L Cr6+ when analytically verified by an independent laboratory. The acute toxicities of chromium to D. pulex differed significantly between laboratories, by almost one order of magnitude. Interlaboratory variability observed in D. pulex tests was attributed to differences in the test organisms' food. As reference toxicant tests, chromium tests are valuable benchmark indices of the relative health of test organisms over time or among laboratories. When toxicity test information is used in critical decision making, such as compliance with effluent permit limitations, a reference toxicant such as chromium contributes to quality control and assurance.

Hexavalent chromium as a reference toxicant in effluent toxicity tests

Water solubility, hydrolysis and photolysis rate constants, and sorption-desorption partition coefficients were determined for lindane in three different natural water-sediment systems, as well as in a Milli-Q water and montmorillonite clay system. The aqueous solubility of lindane in surface waters at 25 ± 1°C ranged from 7.9 to 8.4 mg/L. In Milli-Q water, lindane solubility was 9.2 mg/L. At α = 0.05, no significant difference was found between the values in different natural waters; however, the Milli-Q water solubility did differ statistically. Lindane hydrolysis was found to be catalyzed by hydroxide and hydrogen ions. Neutral hydrolysis was relatively unimportant. Hydrolysis data followed first-order kinetics with kh values of 74 × 10−4 h−1 at pH 9 and 7.4 × 10−1 h−1 at pH 5. Experimental hydrolysis half-life (t1/2) in natural waters of pH 9.3 was comparable to the calculated value (92 h). Other natural water systems of pH 7.3 and 7.8 had t1/2 values greater than calculated values. Adjusted mid-winter photolysis half-life of lindane in Milli-Q water was 1.56 × 103 h. Photolysis rate enhancement was noted in natural water of pH 9.3, possibly due to the alkaline hydrolysis side reaction. Photolysis rate retardation was noted in natural water of pH 7.3 and 7.8. Sorption-desorption coefficient in Milli-Q water-montmorillonite clay was 1,259. Sorption coefficients for the natural systems ranged from 56 to 2,238. Results of the sorption-desorption experiments indicate that the wide diversity of the characteristics of the natural water sediment systems considerably affect the lindane sorption-desorption behavior.

Fate of lindane in the aquatic environment: Rate constants of physical and chemical processes

Effluent toxicity testing is a routine National Pollutant Discharge Elimination System (NPDES) permit monitoring requirement for many municipal and industrial dischargers. Effluent toxicity compliance limits are being set in an increasing effort to limit discharge of toxics into U.S. water bodies. To that end, hazard assessment principles are being applied to limit discharged toxicity based on instream effects as judged by effluent toxicity, fate and exposure. Uncertainty arises in complying with effluent toxicity limits because of a number of factors, including an unacceptably toxic effluent, error in conducting a specified test, test organism health, statistical variability and interferences in the test solution that mask the toxic effect.

Three factors that may influence compliance with toxicity limits and/or identification of toxics are discussed. These factors indicate the need for additional consideration before setting permit limits, determining requirements for toxicity reduction and possibly implementing additional effluent treatment.

Comparisons between reference toxicant data and control mortality showed that reference toxicant data provide an additional control for determining whether effluent toxicity test results are valid and that they can be used to test regulatory compliance. Statistical sampling theory was explored to determine compliance with an effluent toxicity requirement of 80% survival in 100% effluent. Third, several test species were used to determine the causative toxic agents in order to correctly identify toxicity and to separate true toxic effects from interferences in exposures to receiving water.

Variability associated with identification of toxics in national pollutant discharge elimination system (npdes) effluent toxicity tests

The comparative acute toxicity of potassium chromate and dichromate salts to six aquatic species including both freshwater and marine forms was investigated. A thermodynamic equilibrium model was developed to aid in interpreting toxicity data with respect to hexavalent chromium speciation. Although parallel acute toxicity tests conducted with both salts yielded similar LC50 values, toxicity differences tended to become more pronounced as the sensitivity of the test species to the chemical decreased. Observed changes in pH and predicted changes in chromium speciation that occurred between the two salts in tests with less sensitive species were postulated to explain these findings. The implication of the aqueous chromium species to the relative toxicity of the hexavalent chromium are discussed. If hexavalent chromium is widely adopted as a standard reference toxicant for aquatic toxicity testing then the chromate salt should be used since it does not appreciably alter the initial pH of the dilution water and subsequent speciation to the extent that would be expected if the dichromate salt was employed. Standardization of the source of hexavalent chromium used in reference tests will facilitate intralaboratory comparison of toxicity data.

J. H. Rodgers

Papers

Hexavalent chromium as a reference toxicant in effluent toxicity tests

Fate of lindane in the aquatic environment: Rate constants of physical and chemical processes

Variability associated with identification of toxics in national pollutant discharge elimination system (npdes) effluent toxicity tests

Comparative toxicity and speciation of two hexavalent chromium salts in acute toxicity tests

A Model for Predicting the Influence of Suspended Sediments on the Bioavailability of Neutral Organic Chemicals in the Water Compartment