Acute toxicity and ecotoxicological risk assessment of rice pesticides to Lithobates catesbeianus tadpoles

The objective of this study was to determine the acute toxicity of some pesticides used in irrigated rice farming to Lithobates catesbeianus tadpoles. The LC_50-96h for commercial formulations containing bentazon, penoxsulam, vegetable oil, permethrin and carbofuran, separately and their mixtures, were determined at the proportions commonly used in the field. The limits of risk concentrations of these products for the studied species were also established. The LC_50-96h for tadpoles was 4,530 mg L^?1 for bentazon; 7.52 mg L^?1 for penoxsulam + 145.66 mg L^?1 of vegetable oil; 81.57 mg L^?1 for vegetable oil; 0.10 mg L^?1 for permethrin; 29.90 mg L^?1 for carbofuran (active ingredients), and 38.79 times the dose used in the field for the mixture of these products. The environmental risk was determined only for permethrin, and care should be taken when using the vegetable oil.     

Decarboxylation and alkaline colour fading reactions in presence of humic substances

Humic substances (HSs) can substantially influence velocity of reactions in the environment as shown on example of decarboxylation and alkaline colour (e.g., malachite green and crystal violet) fading reactions. In colour fading and decarboxylation reactions of 6-nitrobenzisoxazole-3-carboxylic acid HS act as inhibitors, but additions of surfactants change the pattern of reaction. The inhibitory activity of HSs much depends on their origin. The velocity of studied reactions depends also on pH, temperature and concentration of HS used. Possible micellar catalysis mechanism has been suggested.     

Trends of natural organic matter concentrations in river waters of Latvia

This study revealed significant (P?相似文献   

Sedimentary humic substances from lakes in Latvia

Humic and fulvic acids, isolated from sediments of lakes in different trophic states (Latvia) were studied. The humic substances (HS) were characterized by their elemental and functional composition, their spectral properties, and molecular mass. The humus properties strongly depend on the origin of the sedimentary HS. Substantial similarity between sedimentary HS from oligotrophic and dystrophic water bodies was found, unless the biology of these lakes greatly differs. Humic molecules from sediments of oligotrophic and dystrophic lakes are smaller, more uniform, and contain lower amounts of carboxyl- and hydroxyl-groups than HS from meso- and eutrophic water bodies. On the other hand, sedimentary HS from meso- and eutrophic lakes are dominated by aliphatic structures, and, possibly chromophore groups are present, and they are rich in polar groups. The macromolecules of HS from meso- and eutrophic lakes show the highest polydispersity.     

1980～2000年拉脱维亚和里加的水质变化:希望与问题

本文研究了由于社会经济变革而发生的拉脱维亚环境水质的长期变化(内陆水域的化学成分、废水处理以及饮用水处理作法及质量).为了确定在最近进入表层水域的污染排放物,特别是营养负荷减少之后所发生的变化,还研究了水的成分,影响水化学的主要因素以及人为影响(废水负荷).1991年后(拉脱维亚于1991年重新独立),主要由于来自点源和非点源的营养物负荷的减少以及在环境保护领域的巨大努力,内陆水质开始改善.但是饮用水处理方面的情况则不同,因为在1980年到2000年整个阶段饮用水处理的习惯作法也发生了变化.更严格的饮用水水质标准以及有关配水网中水质变化的新见识使得有必要进一步改进公共供水并把这一特殊的水问题列为拉脱维亚最优先考虑的事项之一.     

Arsenic removal using natural biomaterial-based sorbents

Arsenic contamination of water is a major problem worldwide. A possible solution can be approached through developing new sorbents based on cost-effective and environmentally friendly natural biomaterials. We have developed new sorbents based on biomaterial impregnation with iron oxyhydroxide. In this study, raw peat material, iron-modified peat, iron-modified biomass (shingles, straw, sands, cane and moss) as well as iron humate were used for the removal of arsenate from contaminated water. The highest sorption capacity was observed in iron-modified peat, and kinetic studies indicated that the amount of arsenic sorbed on this material exceeds 90 % in 5 h. Arsenate sorption on iron-modified peat is characterised by the pseudo-second-order mechanism. The results of arsenic sorption in the presence of competing substances indicated that sulphate, nitrate, chloride and tartrate anions have practically no influence on As(V) sorption onto Fe-modified peat, whereas the presence of phosphate ions and humic acid significantly lowers the arsenic removal efficiency.     

Humic substances as surfactants

Humic substances from soils and sediments can be defined as surface active substances based on the surface tension measurements. Although there are several micellar structural models of humic substances currently available, few studies evaluating humic substances as surfactants have been conducted to date. Therefore, we evaluated the ability of humic substances and their derivatives to influence surface tension. We found that the ability of a humic substance to influence the surface tension of a solution depends on its origin. Many industrially produced humic materials exerted little or no impact on surface tension, whereas humic substances isolated from natural environments (water, soil, peat, sediments, sludge from wastewater treatment facilities) exerted a large impact on surface tension. These findings indicate that the modification of humic substances can enable their use as surfactants. In addition, these findings indicate that solutions of humic substances and their derivatives can be used to increase the solubility of organic compounds.     

Growth responses of Scots pine to climatic factors on reclaimed oil shale mined land

Afforestation on reclaimed mining areas has high ecological and economic importance. However, ecosystems established on post-mining substrate can become vulnerable due to climate variability. We used tree-ring data and dendrochronological techniques to study the relationship between climate variables and annual growth of Scots pine (Pinus sylvestris L.) growing on reclaimed open cast oil shale mining areas in Northeast Estonia. Chronologies for trees of different age classes (50, 40, 30) were developed. Pearson’s correlation analysis between radial growth indices and monthly climate variables revealed that precipitation in June–July and higher mean temperatures in spring season enhanced radial growth of pine plantations, while higher than average temperatures in summer months inhibited wood production. Sensitivity of radial increment to climatic factors on post-mining soils was not homogenous among the studied populations. Older trees growing on more developed soils were more sensitive to precipitation deficit in summer, while growth indices of two other stand groups (young and middle-aged) were highly correlated to temperature. High mean temperatures in August were negatively related to annual wood production in all trees, while trees in the youngest stands benefited from warmer temperatures in January. As a response to thinning, mean annual basal area increment increased up to 50 %. By managing tree competition in the closed-canopy stands, through the thinning activities, tree sensitivity and response to climate could be manipulated.     

Research review trends of food analysis in Latvia: major and trace element content

The current paper involves overview of several studies concerning quantitative major and trace element analysis of different food samples, such as products of plant origin, e.g., locally grown vegetables (carrots, onions, potatoes) and products of animal origin derived with or without processing (cottage cheese, eggs, honey). Food samples were collected over the territory of Latvia in the time period 2009–2012. Sample pre-treatment was chosen according to the product specifics but mostly wet mineralization with concentrated nitric acid was applied. Analysis of major elements (e.g., Ca, Fe, K, Mg, Na) and trace elements (e.g., As, Cd, Co, Cr, Cu, Ni, Pb, Se, Zn) was performed by appropriate quantitative analytical technique: atomic absorption spectrometry, inductively coupled plasma mass spectrometry or total reflection X-ray fluorescence spectrometry. Not only the influence of environmental factors (e.g., geographical or seasonal impact) was detected in element dissemination in food, also botanical origin (if applicable) and applied agricultural praxis, product processing and storage specifics were found to be important. Possible food contamination by potentially toxic elements can be associated mostly with the consequences of anthropogenic activities. The studies revealed the significance of food research in the context of environmental science.