A Qualitative Study of Residual Pesticides on Cotton Fibers

Two different methods are utilized for this study. The first method covers the measurement of bioelectrical signals caused by enzymatic inhibition of acetyl cholinesterase (AChE) for the detection of pesticides. Biosensor toxicity analyzer (BTA) was used for the testing and the monitoring of changes in bioelectrical signals caused by the interaction of biological substances, and residues were evaluated. The second method is based on measurement of the oxygen level caused by photosynthetic inhibition of residual pesticides by the interaction with green algae, Scenedesmus (Chlorophyta). Algae growth analyzer (AGA) equipped with miniature sensitive oxygen electrode, a light source and cover to model light and dark phases was used enabling us to follow the lifecycle of algae producing oxygen. The test, conducted under the guideline of faster analogy of DIN 863 toxicity test, alga growth inhibition test (OECD TG 201) was and ISO standard (ISO: 8692). Two samples of cotton were analyzed. Cryogenic homogenization was carried out for sample pretreatment. Soxhlet extraction method (SOX) and ultrasound assisted extraction (USE) were used for extraction. Both methods show reasonable results and can successfully be utilized for the detection of residual pesticides on different types of cotton and especially to compare the classical conventional and organic cotton.

The effect of field-collected biofilms on the toxicity of copper to a marine microalga (Tetraselmis sp.) in laboratory bioassays

Standard algal growth rate inhibition bioassays can lack environmental realism and may over- or underestimate metal bioavailability in natural systems. In aquatic environments, algal species interact with other biota, including other algae, bacteria and biofilms. In this work, the feasibility of incorporating marine biofilms into 72 h algal growth inhibition toxicity tests was explored. The effects of copper on Tetraselmis sp. were tested in the absence and presence of characterised field-collected biofilms. We hypothesised that the addition of biofilm would prevent copper toxicity to the alga primarily through interactions of the metal with other cells and biofilm exudates. The sensitivity of Tetraselmis sp. to copper (based on 72 h IC50 values; the copper concentration to inhibit population growth by 50%) in the presence of a blended biofilm inoculum varied 2-fold and was independent of the amount of biofilm added. However, increases in IC10 and IC20 values indicated some amelioration of copper toxicity. When intact biofilms were added to the bioassays, amelioration of toxicity was more consistent, probably due to increased binding of copper to cell surfaces or exudates. Difficulties in characterising biofilms and distinguishing that material from the test alga need to be overcome before biofilms can be routinely incorporated into laboratory bioassays.

Development and application of a simple procedure for toxicity testing using immobilized algae

A simple microplate technique was adopted for toxicity assessment of a number of pesticides including six herbicides (Atrazine, Dichloroprop, Glyphosphate, Chlorsulfuron, MCPA, and Simazine), an insecticide (Dimethoate) and a fungicide (Propiconazol). Growth response of free and immobilized cultures of the green chlorococcal algae Selenastrum capricornumtum to different treatments of these pesticides was tested and compared. The biotests were carried out under conditions optimal for the growth of the test alga. Algal growth was exposed in terms of dry weight, and was employed as the toxicity-response parameter. Dose-response curves were used to calculate the toxicity of the tested compounds in terms of EC50. Based on EC50 values, the responses of both immobilized and free cultures were quite similar for almost all the treatments. The technique facilitated the visual detection of the lowest toxic concentration giving no detectable algal growth (EC100). The technique is quite simple, rapid, practical, accurate, and space saving. It suggested that batteries of immobilized algae could replace free cultures in studies of toxicity testing.