Effect of farm management practices in the Bt toxin production by Bt cotton: evidence from farm fields in China

Based on farm field plot level survey data and laboratory test, we examine the determinants of the expression of Bt toxin in China’s Bt cotton production. The results show that the expression of Bt toxin differs significantly among varieties. Even for the same variety the expression of Bt toxin also varies substantially among villages and among farmers in the same village. Econometric analyses show that after controlling for the effects of varieties and locations (or villages), farm management, particular applications of phosphate and potash fertilizers, and manure, has significant positive effects on Bt toxin expression in farmer’s fields. In contrast to previous studies which showed that nitrogen fertilizer has a positive impact on expression of Bt toxin, this study shows that nitrogen fertilizer has no significant impact on expression of Bt toxin in farmer’s fields. On the other hand, the expression of Bt toxin has a positive relationship with phosphate fertilizer, potash fertilizer and manure application.     

Buffer strip width and agricultural pesticide contamination in Danish lowland streams: Implications for stream and riparian management

According to the European Water Framework Directive, member states are obliged to ensure that all surface water bodies achieve at least good ecological status and to identify major anthropogenic stressors. Non-point source contamination of agricultural pesticides is widely acknowledged as one of the most important anthropogenic stressors in stream ecosystems.We surveyed the occurrence of 31 pesticides and evaluated their potential toxicity for benthic macroinvertebrates using Toxic Units (TU) in 14 Danish 1st-and 2nd-order streams in bed sediments and stream water during storm flow and base flow. Total pesticide concentrations and toxic potential were highest during storm flow events with maximum TU ranging from −6.63 to −1.72. We found that minimum buffer strip width in the near upstream area was the most important parameter governing TU. Furthermore, adding a function for minimum buffer strip width to the Runoff Potential (RP) model increased its power to predict measured TUs from 46% to 64%. However, including a function for tile drainage capacity is probably equally important and should be considered in future research in order to further optimise the RP model. Our results clearly emphasise the importance of considering buffer strips as risk mitigation tools in terms of non-point source pesticide contamination. We furthermore apply our results for discussing the minimum dimensions that vegetated buffer strips should have in order to sufficiently protect stream ecosystems from pesticide contamination and maintain good ecological status.     

农田景观和管理方式对稻田系统植物多样性的复合影响

农田生物多样性对于维持农田生态系统服务功能和农业可持续发展具有重要意义.为揭示农田景观特征和管理方式对农田生态系统植物群落和物种多样性的影响,以有机稻田(ON)、常规化防稻田(天然林脚下,CN)、常规化防稻田(距天然林>10km,CF)系统为研究对象,调查了田内、田埂和沟渠生境的植物物种组成和多样性特征,并对三种类型稻...     

Modular estuarine mesocosm validation: ecotoxicological assessment of direct effects with the model compound endosulfan

This study represents the first in a series of validation experiments for the modular estuarine mesocosm testing direct pesticide effects. Endosulfan, an agricultural insecticide, was selected as a model contaminant for studying direct toxic effects as well as uptake of this model contaminant by estuarine biota. The grass shrimp, Palaemonetes pugio, and the mummichog, Fundulus heteroclitus, showed significant mortality (96 h LC₅₀: 0.12 and 2.2 μg/l, respectively) to endosulfan as predicted by laboratory bioassays. There was no effect on fiddler crabs and eastern oysters. The mesocosm was also useful in demonstrating the bioconcentration of endosulfan by eastern oysters (bioconcentration factor [BCF]=375) similar to results reported in field studies. This study illustrates the modular estuarine mesocosms' ability to detect direct effects of pesticide exposure and the uptake of a pesticide by estuarine fauna.     

水环境毒物污染点源的生态风险管理现状与展望

评述了发达国家和我国在这一领域的进展和前景。目前国内外常用的基于水质标准／废水排放标准的特征化学污染物法,并不能有效控制组分复杂的废水中的有机毒物排放。因此,仅应用这一传统方法对水环境有机毒物污染点源难以实现有效的生态风险管理。同时采用全废水的生态毒性法可就弥补这一缺陷,根据生态风险管理要求可有效控制组份复杂的废水中有毒有机污染物的排放。鉴别出导致废水生态毒性的关键有机毒物的毒性鉴别评价,是毒物污染点源的生态风险管理核心。本文还对毒性鉴别评价方法学的发展以及全废水毒性法应用于我国水环境毒物污染点源生态风险管理的前景作了评述。     

Fatty acid profiling as bioindicator of chemical stress in marine organisms: A review

The development of industrial, anthropogenic, and agricultural activities is the main factor leading to contaminants’ increasing in marine ecosystems. Contaminants include the great variety of pesticides and heavy metal pollutants. One of the major environmental concerns about herbicides and heavy metals contamination is their bioaccumulation in the ecosystem's primary producers and its subsequent propagation through the trophic chain. Over the last decades, the use of biochemical markers considerably contributed to the evaluation of contamination hazards. The fatty acid composition proved to be a good bioindicator to assess contamination levels. This paper provides a review of current knowledge on the fatty acids response in marine species after exposure to the chemical stressors including organic and inorganic pollutants, mainly pesticides and heavy metals. This review underlines the consistent directional trends in changes of saturated fatty acids, monounsaturated fatty acids and polyunsaturated fatty acids, and summarizes the mechanisms of action leading to their alteration and possible consequences of these changes to marine species from different trophic levels.     

Effectiveness of best management practices in improving stream ecosystem quality

Implementation of best management practices (BMPs), such as improved manure storage, buffer strips, and grassed waterways, through government funded conservation programs is a common approach for mitigation of the impacts agricultural activities have on the surrounding environment. In this study, we tested the ability of these practices to meet the environmental goal of improved stream quality at a “micro-basin” scale in the Upper Thames River Watershed, southern Ontario, Canada. Micro-basins were first and second order basins, averaging 400 ha in area, representing gradients of land cover, geomorphology, and participation in conservation programs. At the outflow of each micro-basin the benthic macro-invertebrate community was sampled, water chemistry measurements completed, and habitat quality assessed. Results showed micro-basins with relatively high levels of BMP implementation consistently demonstrated improved stream ecosystem quality over the majority of micro-basins with low or no implementation. Streams in the Upper Thames River basin appeared to exhibit a threshold effect, where with several BMPs in the same basin an improvement in stream ecosystem quality is visible. In addition to the BMPs implemented through government funded conservation programs, the observed ecosystem improvements are probably due to increased environmental awareness and improved management by farmers. Handling editor: K. Martens     

从水环境角度探析农田氮素流失及控制对策

综述了国内外关于农田氮素流失对水体影响现状、农田氮素流失途径、流失机理及其控制方法等的研究进展及其控制对策.在控制氮素流失对水环境影响方面,针对氮素地表径流流失和淋溶流失采取有效措施,减少氮素对地表水和地下水污染.氮素污染的治理关键是切断氮源和流失途径的联系,应根据氮污染源的等级划分因地制宜地采取治理措施,制定适合我国国情的BMPs(最佳管理措施)管理模式.     

Integration of soil solarization with chemical, biological and cultural control for the management of soilborne diseases of vegetables

The long-term effectiveness of soil solarization integrated with (integration of pest management [IPM]) a biological control agent (Trichoderma virens), chemical fungicide (pentachloronitrobenzene [PCNB]), organic amendment (chicken litter) or physical method (black agriplastic mulch) to reduce southern blight (Sclerotium rolfsii) and southern root-knot diseases (Meloidogyne incognita) were evaluated on vegetable production. Results showed that the long-term effectiveness of IPM plus soil solarization reduced soilborne diseases of vegetables more than two years following the termination of solarization. These disease management strategies in 1991 and 1992, following soil solarization in 1990, reduced the numbers of sclerotia in the soil, and the number of plants killed by southern blight and root-knot of tomatoes, compared to nonsolarized bare soil treatment. The integration of a reduced dosage level of PCNB or T. virens in field plots, reduced southern blight of tomatoes by 100% and 71%, respectively, in solarized soil, compared to nonsolarized bare soil two years following soil solarization. PCNB effectively controlled southern blight in nonsolarized bare soil both years. All solarized treatments, except PCNB plus solarized soil increased tomato yields compared to nonsolarized bare soil plots. In the second study (1992) following soil solarization in 1991, the effectiveness of solarized bare soil, and nonsolarized bare soil mulched with black agriplastic film, with or without Reemay spunbounded polyester row cover, were effective in reducing root-knot of tomatoes as indicated by the root-knot gall index. Following a one year fallow period in 1994 three years following soil solarization, the root-knot gall index for severity of tomato roots grown in solarized bare soil, nonsolarized bare soil, black agriplastic mulched bare nonsolarized soil and black agriplastic mulched solarized bare soil, were 1.0, 3.0, 3.0 and 2.0, respectively, on a 0–5 scale, where 0=0% and 5=100% root-knot galled. In the third study 1992 and 1993, different dosage levels of chicken litter were used to amend soil artificially infested with sclerotia of S. rolfsii at different depths following solarization, decreased the number of viable sclerotia by 85–100%. All solarized treatments and nonsolarized bare soil amended with 18.8 MT/ha of chicken litter, were effective in controlling southern root-knot damage, and postharvest storage root rots of sweetpotato storage roots (Fusarium root rot [Fusarium solani] and Java black rot [Diplodia tubericola]). Our study showed that all soil solarization treatments, and soils amended with chicken litter, stimulated a shift in the soil microbial population dynamics. Rhizobacteria of Bacillus spp. and fluorescent pseudomonads increased significantly in the rhizosphere, rhizoplane, and interior root tissues of tomatoes and sweetpoatoes, grown in solarized soil compared to nonsolarized soil. These microorganisms may have contributed to the increased growth response of vegetables and some were probably suppressive to soilborne diseases     

Runoff characteristics in a small mountain basin analyzed by the use of hydrogen and oxygen stable isotopes

The hydrograph of a small drainage basin was separated into the components of direct runoff, soil water runoff, and ground water runoff, by a method using a stable isotope (¹⁸O and deuterium) to analyze its hydrological characteristics. It shows that the direct runoff consists of rainwater during the event, soil water runoff originating from the latest rainwater before the event, and groundwater runoff is a perfect mixture of rainwater brought to the catchment throughout the year. If these water masses constitute a triangle on a δD–δ¹⁸O diagram, they are independent of each other, and the separation gives a unique result. A comparison of the above results with the hydrograph separation in terms of the response time using a tank model led to an estimation of the flow path and dynamics of each runoff component. This study investigates the mixing process involved with these runoff components and, further, identifies physical properties to be observed in the field to provide for a more detailed analysis of the runoff process. Received: December 6, 1999 / Accepted: May 9, 2000     

Fate of benzyladenine metabolites extracted from tomato shoots in biological systems

The metabolism of radioactive metabolites of BA, obtained from tomato shoots, and purified by chromatographic techniques, was studied in rootless tomato shoots and soybean callus. There is apparently a great deal of interconversion between BA, BAR and BARMP. From the present results it is not possible to determine whether BARMP is formed directly from BA or whether BAR serves as an intermediate in its production. Irrespective of the metabolite applied, the principal metabolite formed in all instances had a retention time of 51 min following HPLC separation. This metabolite was itself not metabolized to any great extent by either tomato shoots or soybean callus. In contrast to tomato shoots this metabolite was not formed when a radioactive metabolite tentatively identified as BAR, was applied to soybean callus.Abbreviations AAW acetic acid: water - BA benzyladenine - BAR benzyladenosine - BARMP benzyladenosine-5-mono-phosphate - TEA triethylamine     

Soil temperature in a sugar-cane crop as a function of the management system

Air and soil temperatures are, by far, the most important state variables of agroecosystems. In the case of sugar-cane (Saccharum officinarum L.) they affect plant development, maturation and a series of biological and physical-chemical soil processes. This paper presents a comparative study of three management practices, applied to the first ratoon of a sugar-cane crop established on a Rhodic Kandiudox (Terra Roxa Estruturada) of Piracicaba, SP, Brazil. The management practices are: (i) interrow with bare soil; (ii) trash mulching, maintaining harvest residues (straw+tips) on the soil; (iii) soil with residues from burning the prior crop. Soil temperature was measured with digital stick thermometers driven into the soil down to the depths of 0.03, 0.06 and 0.09 m, meter by meter, close to the crop row, along an 84-point transect that covered all treatments and borders. The measurements were performed from November 1998 (right after the first harvest of the planted cane) to June 1999. The effects of the treatments on soil temperature were, evidently, more prominent in the period November/February when the plants had a smaller height, not closing interrows. Data that were collected on typical days, chosen along the development cycle of the crop, always from 11:00 to 12:00 a.m., show significant differences, mainly between mulched and non mulched treatments, reaching values as high as 7 °C for the average of the three depths. A comparative analysis is made between treatments and their effects are discussed in relation to the sugar-cane crop.     

Field assessment of soil biological and chemical quality in response to crop management practices

Soil microbiological and chemical aspects were evaluated to determine the effects of conservation tillage and crop rotation on soil fertility over a 16-year period. A field trial was established to compare two cropping systems (continuous soybean and maize/soybean, soybean/maize rotation). In addition, maize (Zea mays L.) and soybean (Glycine max L., Merr) were grown in two different tillage systems: no tillage and reduced tillage. Soil populations of Trichoderma spp., Gliocladium spp. and total fungi were more abundant when maize or soybean were under conservation tillage and in the maize/soybean and soybean/maize rotation, than in continuous soybean. Furthermore, higher levels of microbial respiration and fluorescein diacetate hydrolysis (FDA), were recorded under no tillage systems. However, soil counts of Actinomycetes and Pythium spp., and Pythium diversity together with soil microbial biomass were not affected by the field treatments. To establish a correlation with soil biological factors, soil chemical parameters, such as pH, organic matter content, total N, electrical conductivity, N–NO₃ ⁻ and P were also quantified, most of the correlations being significantly positive. Under no tillage there was a clear increase of the amount of crop residues and the C and N soil content due to the presence of residues. Also the distribution of crop residues in surface soil due to zero tillage and the quality of these residues, depending on the crop rotation employed, improved on soil biological and chemical characteristics. Crop yield was also enhanced by zero tillage through the management of residues. Although yield values were not directly associated with the development of microorganisms, both yield and microorganisms were influenced by crop management. These results suggest that measuring soil properties over a long period helps to define effective management strategies in order to preserve soil conditions.     

Chromium in the environment: factors affecting biological remediation

Chromium, in the trivalent form (Cr(III)), is an important component of a balanced human and animal diet and its deficiency causes disturbance to the glucose and lipids metabolism in humans and animals. In contrast, hexavalent Cr (Cr(VI)) is highly toxic carcinogen and may cause death to animals and humans if ingested in large doses. Recently, concern about Cr as an environmental pollutant has been escalating due to its build up to toxic levels in the environment as a result of various industrial and agricultural activities. In this review, we present the state of knowledge about chromium mobility and distribution in the environment and the physiological responses of plants to Cr with the desire to understand how these processes influence our ability to use low cost, environmentally friendly biological remediation technologies to clean up Cr-contaminated soils, sediments, and waters. The use of biological remediation technologies such as bioremediation and phytoremediation for the cleanup of Cr-contaminated areas has received increasing interest from researchers worldwide. Several methods have been suggested and experimentally tested with varying degrees of success.     

Insect pest management in African agriculture: Challenges in the current millenium

Pest management on a global scale experienced a total revolution after World War II when synthetic organic compounds were in agriculture and public health. However, it soon became apparent that there were many limitations in the use of chemicals for pest management. In agriculture, problems of pest resurgence, secondary pest outbreaks, pest resistance and adverse effects of pesticides on the environment, including human poisoning and toxicity to other non-target organisms, led to the search for alternative approaches to the pest outbreak problem. The 1960s produced new ideas on integrated pest management (IPM) strategies, followed by intensification of the search for biological control agents, which could be incorporated into IPM programmes. New application technologies were developed in the 1970s and 1980s and ecological approaches to the pest problem were spearheaded in the developed world in the 1990s, with extensive studies focused on the whole ecosystem. Important advances in crop production have also taken place in Africa in this century, involving adoption of high yielding varieties, fertilizer application, intensification of crop protection approaches, less shifting cultivation and more mono-cropping systems. However, these advances have led to increasing pest problems which unless tackled imaginatively and intelligently, they could become the most important constraint in crop production in the present millennium. Africa has entered the current millennium with relatively underdeveloped agriculture on a global scale and little investment in research on new pest management technologies that could be used to reduce crop losses. We are still highly dependent on pesticides for pest management. Therefore, the greatest challenges in agriculture in Africa will be the switch from a pesticide based mode of reducing losses due to pests to one that is ecosystem based, making use of insect management techniques which are ecologically and economically sound. Specifically, some of the major challenges in pest management in agriculture in Africa include; (i) reducing the dependence on pesticides, thus avoiding the limitations observed in the past 50 years; (ii) overcoming ignorance of the pest species and their associated community of parasites and predators which has dire consequences on the whole ecosystem; (iii) keeping out exotic pests, which in this millennium have had a devastating blow on the production of some crops and (iv) developing indigenous technologies for pest management (IPM, biocontrol, etc.) and making available to farmers materials for pest management which are affordable, safe, effective and environmentally friendly (e.g. microbial, botanicals, pheromones, genetically engineered products etc.). Both legislative and quarantine measures will have a significant role to play in pest management in the next millennium, but only when practised on a wider geographical area. Information technology (IT) will affect the way we acquire and make use of pest management strategies. Africa is therefore faced with the challenge of building up and improving its infrastructure and expertise on IT if it is to benefit pest management on the continent.     

Studies on the fungi associated with tomato fruit rots and effects of environment on storage

Seven fungi associated with fruit rot of tomato were isolated includingFusarium equiseti, F. chlamydosporum, Alternaria solani, Geotrichum candidum, Acremonium recifei, Aspergillus flavus andA. niger. They were all pathogenic on tomato fruits, most pathogenic beingGeotrichum candidum followed byA. niger. Least rot was caused byAlternaria solani. The optimum temperature for maximum rotting caused byG. candidum, A. niger andA. flavus was 30°C. The relative humidity for maximum rot ranged from 70–90%. Tomato fruits stored well at 0–10°C and rather poorly at 20–30°C. Fruits stored at 35°C showed blemishes. The best RH for storage ranged between 60 and 90%.     

Benzidine-based dyes: effects of industrial practices,regulations, and world trade on the biological stains market

One of the most sweeping changes in the dye industry since the advent of synthetic dyes grew out of the health risks associated with benzidine. Dyes made from benzidine and its derivatives were used around the world until adverse health effects become incontrovertible. Workers and family members of workers involved in production and use of benzidine-based dyes had a high incidence of bladder cancer. Following publication of several reports documenting this health hazard, dye makers in the USA, Europe, and Japan phased these dyes out of production in the 1970s. Government regulations lent legal support for these voluntary initiatives. Two strategies subsequently evolved to compensate: developed nations brought alternative substances to market while emerging countries increased production of carcinogenic dyes and sold them at discount prices around the world. Nearly all dye manufacturing now has moved away from nations whose costs of production and compliance rendered them unable to compete. The purpose of this brief review is to publicize the health risks associated with dyes made from benzidine and its congeners, and to alert all companies and end users handling these dyes for biomedical applications that composition of the product and lot-to-lot variability may be problematic because of the manufacturing and distribution practices of the countries where they are produced.