No abstract

Basic principles for assessing phytotoxicity are the same whether the test compound is a heavy metal, herbicide, fungicide, insecticide or other toxic compounds. The difference lies not in the method of evaluation, but in the experimental program and working methodology. In this paper the phytotoxic effects of heavy metals, Cr (VI) and Cd (II) on plants germination and growth were studied. Stock solutions of the two heavy metals were prepared at a concentration of 1000 mg/L, in distilled water. Diluted working solutions were prepared for experiments, with the following concentrations: 30, 60, 90, 120, 150 and 300 mg/L. Heavy metal solutions were used in the phytotoxicity tests, by taking 3 mL for each metal ion, and soaked in Whatman filter paper discs placed in Petri dishes. This way the interaction between the liquid phase in soil (soil solution) in which various concentrations of heavy metals are dissolved and the environmenta (in particular the vegetation) are simulated. Lepidium sativum was used as test plant, by conducting germination tests for three days of exposure. Lepidium sativum is a sensitive test species, widely used in the toxicity tests because it is rapidly growing, it is cheap and easy to analyze. The seed germination, root length and dry biomass of plants were assessed. It was found that metal ions have inhibitory effect on seed germination process of L. sativum. Root development is affected by both the tested metal ion and its concentration. The dry biomass reflects the toxicity of metal ions tested, which is dependent on the type of metal ion and its concentration. The study shows that the tested plant experiences a important toxicity stress due to the exposure to heavy metals.

Chromium and cadmium are heavy metals that occur naturally in the environment and especially in soils. Their toxic effect is more pronounced at high concentrations and it depends on the oxidation states. While Cr (III) is considered an essential trace element for the metabolism of living organisms, Cr (VI) has a higher mobility and is easily soluble in soils and can be leached into surface water or groundwater, and taken up by plants. That leads to a toxic and carcinogenic effect to humans via inhalation for long exposures. The concentrations and the form of heavy metals in soils and the behavior of their free ions in soils solution are influenced by soil pH, organic matter (OM) content, cation exchange capacity (CEC), and clay mineralogy. This work presents the toxicity effect of two common heavy metals that can be found in soil (chromium and cadmium) on two microbial strains, which are also isolated from soil: Azotobacter sp. and Pichia sp. Batch tests where made using different concentrations of the selected heavy metals and culture medium: for Azotobacter sp. strain was used a Sabouraud medium and for Pichia sp. strain a YEPD medium (Yeast Extract, Pepton, Dextrose). The dry weights of the microbial culture were used to determine the microbial growing, calculated in percent inhibition of dry weight versus concentrations of metal ions.

The potential of using ultrasonic irradiation and microbiological treatment for the removal bis(1-chloro-2-propyl) ether from aqueous solutions has been investigated. Experiments were performed in a continuous bioreactor, 3500 mL volume, and in an ultrasonic bath respectively, using frequencies of 38+1kHz and applying a power of 30 W. Under these conditions, the sonochemical conversion of ether was found to be superior to the biological one. The ultrasound method was improved by air bubbled into liquid bulk solution and it was found that the main part of bis(1-chloro-2-propyl) ether destruction takes place in the close vicinity of the ultrasound source. These experiments showed the usefulness of the applications of ultrasound to the wastewater treatment processes.

In this study, the authors explore the potential of ultrasound and wet catalyzed peroxide oxidation into the wastewater treatment processes. The processes applied for degradation of pesticides were carried out using Fenton reagent and sonochemical treatment. The Fenton and the sono-Fenton decomposition of 2,4-dichlorophenoxyacetic acid (2,4 D), 4-(2,4-dichlorophenoxy)butyric acid (2,4 DB), 4-chloro-o-tolyoxyacetic acid (MCPA), 3,5-dibromo-4-hidroxybenzonitrile (bromoxynil), and 3-(4-chlorophenyl)-1,1-dimethylurea (monuron) showed that, in all cases ultrasound irradiation of wastewater improved the wet oxidation process.