J.M. Carrasco

Effects of pyridaphenthion on growth of five freshwater species of phytoplankton. A laboratory study.

The acute toxicity of the insecticide and acaricide pyridaphenthion to five species of freshwater phytoplankton, Scenedesmus acutus, Scenedesmus subspicatus, Chlorella vulgaris, Chlorella saccharophila and Pseudanabaena galeata was determined. Insecticide concentrations eliciting a 50% growth reduction over 96 h (EC50) ranged from 2.2 to 30.9 mg/l. The two species of Chlorella and the cyanobacteria P. galeata were more tolerant than the two species of Scenedesmus. Concentrations of pyridaphenthion detected in some natural waters were less than the toxic threshold for these species.

Bioconcentration of the insecticide pyridaphenthion by the green algae Chlorella saccharophila

A study was undertaken to examine the uptake of the organophosphate insecticide pyridaphenthion in the chlorophyta Chlorella saccharophila. Algae cultures were exposed to the initial nominal concentration 10.0 mg l(-1) pyridaphention during seven days. The insecticide bioconcentrates in the biomass to the highest level of 441.5 +/- 25.9 mg kg(-1) on the fifth day of exposure and was followed by a decrease to 76.6 +/- 5.1 mg kg(-1) on the seventh day. A model was constructed to describe the dynamic process, which estimated a bioconcentration factor (BCF) equal to 28. The study demonstrates the potential of accumulation of pyridaphenthion in aquatic organisms and helps to expand the pyridaphenthion toxicity database. The replacement of fenitrothion by pyridaphenthion concerning their use in rice flooded cultures is discussed.

Acute toxicity and bioconcentration of fungicide tebuconazole in zebrafish (Danio rerio)

This research work investigated the bioconcentration of tebuconazole [(±)‐α‐[2‐(4‐chlorophenyl)ethyl]‐α‐(1,1‐dimethylethyl)‐1H‐1,2,4‐triazole‐1‐ethanol] fungicide in zebrafish (Danio rerio) under laboratory conditions and a first‐order kinetic pesticide dissipation in the water. The concentrations of tebuconazole fitted to an equivalent nonlinear kinetic type model which allowed the calculation of the following parameters: bioconcentration factor (38.80 L kg−1), time to reach maximum fish concentration (6 days), maximum concentration in fish (0.0075 μg mg−1), half‐life in fish (24 days) and time needed for the fish to eliminate 95% of the maximum concentration (105 days). These calculations permitted the establishment of theoretical reference limit values for human consumption of fish and the establishment of safe limits for the water pesticide concentration. The data would also be useful in safe strategies associated with fishery activities that are conducted in aquatic regions close to crops using tebuconazole. The information will contribute to enlarge the tebuconazole toxicokinetics database of aquatic organisms.

Level IV fugacity model depending on temperature by a periodic control system

Abstract A ‘level IV fugacity model’ depending on temperature, to simulate effects of periodic temperature changes on the dynamic distribution of chemical compounds in environmental systems is presented. This model is a continuous time dynamic and periodic control system of a nonsteady-state level IV fugacity model with capacity of fugacity, substance degradation rate, and substance transfer coefficients depending on temperature. Properties of this model as stability and positivity are studied. In order to evaluate the numerical results, a discretization preserving the stability and yielding the positivity of the model is used to simulate and illustrate the dynamic distribution of molinate herbicide in a hypothetical three compartmental environmental system, similar to a paddy field, consisting of air, water and bottom sediment, with four periodic temperature changes. The results show that the discretization preserves the periodicity, stability and the positivity properties. When considering a periodic temperature variation, we observed a significant temperature effect on the capacity of fugacity of compartments of the model. This temperature effect largely affect the dynamic distribution of a chemical compound in environmental systems.

Unsteady state fugacity model by a dynamic control system

Abstract A continuous time dynamic system of an unsteady state fugacity model is presented. Properties of this model as stability are studied. In order to evaluate numerical results a discretization preserving the stability and yielding the positivity property of the model is used. Finally, algorithms to determine the values of the fugacities, the concentrations and the dissipation time are given. The above study is illustrated with numerical results in a three compartmental environmental system.

Fenitrothion and 3‐methyl‐4‐nitrophenol degradation by two bacteria in natural waters under laboratory conditions

Abstract The ability of two bacterial strains, Flavobacterium sp. strain ATCC 27551 and Arthrobacter aurescens strain TW17, to degrade fenitrothion and the product of its hydrolysis 3‐methyl‐4‐nitrophenol (MNP) in natural water samples under laboratory conditions was studied. Fenitrothion was degraded by Flavobacterium sp whereas MNP was not degraded by this strain. In comparison, MNP was metabolized by A. aurescens and fenitrothion was not. The natural microbial populations did not decompose the fenitrothion and MNP, however Flavobacterium sp and R. aurescens degraded these compounds in the presence of the natural microbial population.

Molinate decontamination processes in effluent water from rice fields

The performance of aeration, photodecomposition and biological degradation processes as methods to reduce molinate contamination levels in effluent water from rice fields was studied. Aeration produced a molinate dissipation of 84%, as against 22% without aeration. Application of UV-light to clean water solutions achieved a molinate photodecomposition of 96% in 24 h. Maximal degradation obtained in algal cultures was 55% in 20 days and 78% in 40 days. In micro-organism cultures, kept in darkness and with a continuous flow of aqueous solution of molinate and inorganic salts, a degradation of 97% was achieved.

Level IV fugacity model by a continuous time control system

Abstract A continuous time dynamic control system of the ‘Level IV Fugacity Model’ is presented and applied to selected organic chemicals in evaluative environments system. In order to illustrate the numerical solution by this model a discretization is used to calculate the fugacity, concentration and fugacity settling time for a set of three insecticides applied in a hypothetical three compartmental environmental system. The model employs the fugacity concept and treats three bulk compartments: air, water and bottom sediment. Input to the model consists of a description of the environmental, the physical-chemical and reaction properties of the chemical, and emission rates. Expressions in matrix form are included for emissions, advections, reactions, and inter-phase transference. An algorithm to determine the values of the fugacities, concentrations and fugacity settling time is given.