Comparison and improvement of methods for determining soil dehydrogenase activity by using triphenyltetrazolium chloride and iodonitrotetrazolium chloride

The triphenyltetrazolium chloride (TTC) method described by Thalmann (1968) and the iodonitrotetrazolium chloride (INT) method described by Spothelfer-Magaña and Thalmann (1992), used for measuring soil dehydrogenase activity, have been modified to overcome some methodical short-comings. Absorption maxima of 485 nm for triphenylformazan dissolved in acetone, 491 nm for iodonitrotetrazolium formazan (INTF) dissolved in tetrahydrofuran and 455 nm for INTF dissolved in N,N-dimethylformamide are recommended for measuring wavelengths. Extracting triphenylformazan twice with acetone is less toxic and proved to be at least as efficient as extraction with a mixture of 90% acetone and 10% carbon tetrachloride (Thalmann 1968 method). Tetrahydrofuran and dimethylformamide were equally good in extracting INTF from soils, but the former was less toxic. Anaerobic incubation resulted in the formation of higher amounts of triphenylformazan and INTF as well as reduced standard error. Both TTC and INT reduction showed high reproducibility and good differentiation of the microbial activity of six soils. For several reasons (more easily determined substrate dose depending on different soil types, better reduction, shorter incubation time), INT reduction seems to be a more suitable method of measuring soil microbial activity than TTC reduction.     

微生物菌肥对草原矿区排土场土壤微生物与土壤酶活性的影响

[目的]研究施入微生物菌肥对土壤微生物数量及主要土壤酶活性的影响,为利用微生物菌肥改良草原矿区排土场恶劣土壤环境提供理论依据。[方法]采用完全随机区组设计,设微生物菌肥2种施用方法、3种施用量,对不同施肥处理后土壤中可培养细菌、真菌、放线菌菌落数量进行测定,分析土壤过氧化氢酶活性、蔗糖酶活性、脲酶活性、碱性磷酸酶活性变化。[结果]施用微生物菌肥土壤中可培养细菌、真菌、放线菌菌落数量均显著高于未施肥处理(p0.05);施用微生物菌肥土壤中脲酶、蔗糖酶、碱性磷酸酶、过氧化氢酶活性比未施肥样地分别增加29.0%,92.6%,25.7%,75.7%;土壤可培养细菌、真菌、放线菌菌落数量与土壤酶活性之间有一定的相关性;在微生物菌肥沟施法与较大的菌肥施用量作用下土壤可培养细菌、真菌、放线菌菌落数量较高,土壤酶活性较强。[结论]微生物菌肥添加使草原矿区排土场土壤中微生物菌落数量增加、土壤酶活性增强,施用微生物菌肥改善了原状土壤环境,增加了土壤肥力。     

电子束辐照对小麦储藏抑菌及加工品质的影响

该文研究了不同剂量电子束辐照对储藏小麦微生物菌落的抑制作用,以及辐照后对小麦主要储藏指标与加工品质的影响。试验结果表明,电子束辐照对储藏小麦菌落总数有明显的抑制作用（P＜0.01）,且辐照剂量越高菌落总数越低;不同剂量辐照后,对所有霉菌属的抑制效果均达极显著水平（P＜0.01）。经0～5.1 kGy剂量辐照后,小麦感官及基本营养成分没有太大变化;面团流变学特性表明,除稳定时间和断裂时间随着剂量的增加略增外,评价值与弱化度呈负相关,其他吸水率、形成时间的变化并不十分明显;但高剂量照射使其面筋指数、α-淀粉酶活性迅速降低,经5.1 kGy剂量辐照的比未经辐照的小麦降落数值下降了56.12%。馒头制品品尝评分也随着辐照剂量的增大而降低。     

Teff (Eragrostis tef) production constraints on Vertisols in Ethiopia: farmers' perceptions and evaluation of low soil zinc as yield-limiting factor

Thirty samples of grassland surface soil, which had a diverse management history and consequently displayed a wide range of soil properties, were studied to analyze the relationships between soil microbial activity and soil properties. The microbial measurements included the number of bacteria, number of Gram negative bacteria, number of fungi obtained by the plate method, TTC reducing activity and nitrifying activity. In the uppermost layers (at the 0 to 2 cm depth), Simple correlation analyses showed that bacterial numbers were positively correlated with soil pH and negatively correlated with Bray No. 2 P, total C, and grassland age. TTC reducing activity and nitrifying activity were also positively correlated with soil pH, while the fungal number was not significantly related to any soil properties. In the lower layer (at the 5 to 15 cm depth), all of the microbial measurements were negatively correlated with grassland age and were positively correlated with microbial substrate level. soil pH and exchangeable K were positively correlated with the microbial measurements except for the Gram negative bacteria, and significant correlations among almost all the microbial measurements were observed. These results suggest that soli pH accounted primarily for microbial activities in the uppermost layers. Also microbial substrate level, soil pH and probably amounts of exchangeable K, which inevitably decreased with grassland age, appeared to control the microbial activities in the lower soil layers.     

四川和重庆地区的植茶土壤与茶叶品质

A laboratory experiment was conducted to evaluate the effect of triphenyltetrazolum chloride(TTC) on soil microorganisms and the availability of pH characterization medium in BIOLOG plates.Application of TTC decreased the color development sharply and resulted in a great biocidal effect on the growth and reproduction of soil microorganisms,indicating that TTC can affect the discrimination on soil microbial community.The microtitration plates with 21 cabon sources and two different pH levels(4.7 and 7.0) were used to determine microbial community structure of eight red soils.The average utilization(average well colour development) of the carbon sources in the paltes with different pH levels generally followed the same sigmoidal pattern as that in the traditional BIOLOG plates,but the pH 4.7 plates increased the discrimination of this technique,compared with the pH 7.0 plates.Since most tested soils are acid,it seemed that it‘s better to use a suitable pH characterization medium for a specific spil in the sole carbon source test.     

Einfluß variierter Temperatur und Feuchte auf mikrobielle Aktivitäten im Boden unter Laborbedingungen

Influence of varied soil temperature and moisture on microbial activities under laboratory conditions Under laboratory conditions the influence of temperature (10°C, 20°C, fluctuation from 5° to 30°C within 12 h with additional freezing for 3 days) and soil moisture (30%, 60% w.h.c., remoistening to 60% for 1 week) on several microbial activities was investigated. The biomass-related, glucose-induced short-term respiration and the dehydrogenase activity (TTC reduction) were higher at 10°C in most cases as compared to 20°C. Independent of freezing fluctuating temperature caused the lowest activities. The nitrogen mineralization (including nitrification), however, was affected in the opposite way. No marked influences were observed with β-glucosidase, arylsulfatase, and alkaline phosphatase. In the sandy loam nearly no effects of the soil moisture occurred and in the loamy sand especially the dehydrogenase activity was higher at 30% w.h.c., whereas the nitrogen mineralization was lower. From the results it can be concluded, that ecological conditions favouring mineralization without substrate addition may even reduce microbial biomass by decomposition.     

墙体材料及其组合对日光温室墙体保温性能的影响

堆肥是由群落结构演替非常迅速的多个微生物群体共同作用而实现固体废物资源化、无害化的动态过程。本文在综合国内外文献资料的基础上,结合本实验室的研究工作,从堆肥过程中微生物群落的演替、有机物降解菌的选育应用、变性梯度凝胶电泳(DGGE)在堆肥微生物研究中的应用等方面介绍了现代堆肥过程中微生物研究的进展及存在问题,并且指出堆肥过程中微生物菌系组成变化复杂和实验手段有限是限制本研究的主要因素,今后应重视利用分子生物学方法进行微生物的研究工作,并根据微生物之间的协同关系有目的地构建降解多种有机废弃物的高效稳定复合菌系,以适应复杂的堆肥环境。     

BIOLOG法测定土壤微生物群的一些局限性

Reduction of Cr(VI)to Cr(Ⅲ）were studied in a fresh wheat rhizosphere soil(Kuroboku,high humicandosol) pretreated with a basal fertilizer consisting of (NH4)2SO4,P2O5 and KH2PO4 and with K2Cr2O7 by using a rhizobox system.It was found that rhizosphere exerted a positive effect on Cr(VI) reduction.Part of the reason was the decrwease of pH in the rhizosphere due to application of (NH4)2SO4,implying that application of physiologically acid fertilizers would reduce Cr(VI) toxicity to plants.     

基于高光谱技术的菌落图像分割与计数

在平板菌落计数过程中,菌落与背景区域类似的颜色会干扰菌落的准确计数。为了准确测定细菌数,该研究利用高光谱图像技术捕捉成分差异引起的菌落与背景区域光谱特征,并结合化学计量学方法对平板的菌落进行分割并实现计数。采集枯草芽孢杆菌菌落平板的高光谱图像,提取菌落、背景区域的高光谱信息;利用遗传算法结合最小二乘支持向量机建立菌落区域/背景区域判别模型;随后,将菌落平板高光谱图像中每一个像素点对应的光谱信息代入判别模型以判断属于菌落的区域,模型的识别率为97.22%;最后,利用特征波段下的高光谱图像实现菌落的分割及计数,计数平均相对误差值为4.2 %,用时约为10 min。相比较于计算机视觉计数法,菌落计数法的平均相对误差降低了49.4%,结果表明建立的方法有望成为一类新的准确平板菌落计数方法。     

Microbial biomass and activity in urban soils contaminated with Zn and Pb

Summary The effects of heavy metals on microbial biomass and activity were investigated in 30 urban soils, contaminated mainly with Zn and Pb to different extents, in terms of the physicochemical and biological characteristics of the soils. Evaluated by simple and multiple regression analyses, the microbial biomass was not affected significantly by easily soluble Zn + Pb (extractable with 0.1 NHCI). The biomass was accounted for as a function of cation exchange capacity (CEC), total organic C and the numbers of fungal colonies present (R ² = 0.692). Carbon dioxide evolution from soils, which reflected microbial activity, was studied on soils incubated with microbial-promoting substrates (glucose and ammonium sulfate) or without. Carbon dioxide evolution was negatively related to Zn+Pb, and this inhibitory effect of the metals was greater in the soils incubated with substrates. Carbon dioxide evolution in soils with substrates was closely related to Zn+Pb, bacterial numbers and the numbers of fungal colonies (R ² = 0.718). Carbon dioxide evolution in soils without substrates was accounted for as a function of Zn + Pb, biomass and the C/N ratio (R ² = 0.511). Using these relationships, the effects of heavy metals on soil microorganisms are discussed in terms of metabolically activated and dormant populations.     

滴灌和微生物有机肥对设施土壤呼吸的耦合作用及机制

为研究滴灌水分和微生物有机肥对设施土壤呼吸的影响及耦合作用机制,设计不同灌溉定额(15、18、21 mm)和不同微生物有机肥施用量(2 800、3 600、4 400 kg/hm2)处理,以传统化肥处理为对照,观测滴灌和微生物有机肥协同作用下土壤呼吸速率、累计碳排放量等指标,分析土壤呼吸与土壤温度、湿度、有机质含量、酶(脱氢酶、脲酶和过氧化氢酶)活性及根系生物量之间的互动响应关系。结果表明:滴灌-微生物有机肥处理有利于提高土壤有机质含量和酶活性,土壤脱氢酶、脲酶和过氧化氢酶活性分别提升11.6%～27.6%、8.0%～27.7%和1.8%～11.2%,其中滴灌和微生物有机肥相结合对脲酶活性的影响达到显著(p0.05)水平;土壤呼吸速率与根系生物量、土壤温度和有机质含量呈极显著(p0.01)正相关,与土壤酶活性呈显著(p0.05)正相关。该研究证明了滴灌和微生物有机肥对土壤碳排放有显著的耦合效应,滴灌和微生物有机肥耦合主要通过改变土壤有机质含量和根系生物量,对土壤呼吸产生影响。     

The influence of seabird nutrient enrichment and grazing on the structure and function of island soil food webs

Marine inputs from seabirds (in the form of guano) to terrestrial coastal communities play an important role in supporting aboveground food webs. However, little is known about the importance of seabird-derived nutrient inputs for belowground food webs and their function relative to other factors that regulate belowground communities. Here, we tested the relative importance of nutrient enrichment from seabirds and grazing, a known driver of belowground properties, in determining the structure and function of the soil food web in an island system. This was tested by measuring the size and composition of the microbial community, the abundance of nematode feeding groups and rates of decomposition and net nitrogen (N) mineralisation in soil samples collected from grazed and ungrazed plots at coastal and inland locations, representing sites of high and low seabird influence respectively, on the Isle of May in the Firth of Forth, east Scotland. We found that proximity to seabird breeding colonies, and associated greater input of seabird-derived N, stimulated the size of the soil microbial biomass and the abundance of bacteria relative to fungi in the soil microbial community relative to inland areas that received significantly less N. Despite this, proximity to seabird colonies had no detectable effect on rates of decomposition or N-mineralisation. The short-term removal of mammalian grazers, in the form of rabbits, had only limited effects on the structure of the soil food web, mainly affecting the abundance of bactivorous nematodes which were greater in grazed than ungrazed situations. However, cessation of grazing did impact significantly on rates of N-mineralisation and decomposition, which were higher and lower in grazed than ungrazed situations respectively. In conclusion, our study provides evidence that allochthonous nutrient inputs from seabirds have significant impacts on the composition of the soil microbial community, and that these effects outweigh short-term effects of grazers as a driver of soil food web structure in the island system studied. Overall, our results indicate the important roles that natural sources of N and grazing play as drivers of soil food webs and their function.     

Microbial populations in pullman clay loam receiving large applications of cattle feedlot waste

One way to disperse waste from large commercial feedlots is to spread large amounts of the waste on limited areas nearby. The effects of this practice on the soil microbial populations was assessed. Feedlot waste (FLW) was applied for 5 yr at rates of 0, 22, 67, 134, and 269 t ha^?1 yr^?1. Additional treatments were 538 t ha^?1 yr^?1 for 1 and 3 years and applications of N and NPK fertilizer. Soil cores from plots were sampled for microbial analysis before, during, and after the fifth growing season. April, July. and December soil samples were analyzed to 180-, 20-, and 480-cm depths, respectively. The following utritional and physiological groups of microorganisms were counted: soil fungi on Rose Bengal agar; bacteria on a basal mineral salts medium, on nutrient agar (both aerobically and in BBL GasPak jars), and on EMB agar (Escherichia coli-type colonies and total counts); and nitrifying and denitrifying organisms. Little effect due to FLW application rates was found, and organisms producing coliform-type colonies on EMB agar did not persist in the soil. The results indicated that applying large amounts of feedlot waste will not deleteriously affect soil microorganisms.     

我国有机肥原料及商品有机肥中四环素类抗生素的检出率及含量

  【目的】  畜禽粪便等有机肥是抗生素污染农田土壤的重要源头之一。本研究通过调查分析我国有机肥原料及商品有机肥中四环素类抗生素的检出率及含量,为有机肥的安全施用提供依据。  【方法】  在全国采集有机肥生产的主要原料和辅料样品180个及商品有机肥样品244个,进行土霉素 (OTC)、四环素 (TTC)、金霉素 (CTC) 和强力霉素 (DXC) 4种四环素类抗生素 (TCs) 的分析。  【结果】  4种抗生素的总检出率为24.29%,其中有机肥原料和商品有机肥中的检出率分别为35.00%和16.39%,商品有机肥检出率低于有机肥原料。总样品数中检出1～2种抗生素的样品占80.58%,其中商品有机肥中占92.50%,有机肥原料中占73.02%。4种TCs含量由大到小顺序为CTC (22.11 mg/kg) > OTC (2.49 mg/kg) >TTC (1.74 mg/kg) >DXC (0.71 mg/kg),检出率由大到小顺序为OTC (14.39%) > DXC (11.08%) > CTC (8.96%) > TTC (6.13%)。有机肥原料中4种TCs的检出率由大到小顺序为猪粪 (83.33%) > 鸡粪 (66.67%) >牛粪 (30.77%) >羊粪 (24.42%),在鸭粪、菇渣、油渣 (枯饼)、酵母渣及骨粉中也有检出,说明TCs除了在畜牧养殖业中运用普遍,目前已延伸到蘑菇种植、动物源食品业的下脚料等。羊粪中CTC、TTC及OTC含量较高,猪粪和牛粪中CTC和OTC含量较高。商品有机肥中TCs的去除率分别为OTC (77.81%) >CTC (75.02%) >TTC (72.84%) >DXC (62.80%)。内蒙古和甘肃是4种TCs检出率及含量都最高的地区。  【结论】  有机肥原料和商品有机肥4种常用四环素类抗生素的检出率分别为35.00%和16.39%,总检出率为24.29%,商品有机肥的检出率低于生产原料。抗生素在鸡粪和猪粪及其制备的商品有机肥中的检出率高于其他原料。有机肥的堆肥化过程能去除畜禽粪便原料4种TCs的62.80%～77.81%,去除率由大到小顺序为OTC >CTC>TTC>DXC。     

中国小麦胚芽资源分布及深加工相关品质

粮食加工副产物的深加工与综合利用是中国粮食工业发展的重要方向,为了准确获得中国小麦资源总量、分布以及品质状况,在调查中国小麦胚芽资源分布基础上,从中国小麦主产区的大型面粉企业采集小麦胚芽样品,分析商用小麦胚芽的主要营养组成以及微生物污染状况。结果表明,中国每年实际可利用小麦胚芽约20万t,资源主要集中在山东、河南、河北等省;商用小麦胚芽的平均酸价(以KOH计)22.8mg/g,夏季最高达60.4mg/g;其平均含水率为12.1%、蛋白质质量分数为33.70%(其中赖氨酸质量分数为2.10%)、油脂质量分数为11.12%(其中亚油酸质量分数为58.34%),α-生育酚质量分数为0.23%;其菌落总数平均为2.65×104cfu/g。小麦胚芽资源调查与品质评估结果,对中国粮食工业发展规划和粮食副产物深加工企业决策将具有重要的参考价值。     

我国不同地区杨树根际磷细菌的分离与鉴定

A few soil microorganisms can convert insoluble forms of phosphorus(P) to an accessible form to increase plant yields.The objectives of this study were to isolate,screen and identify the phosphobacteria,i.e.,phosphate-solubilizing bacteria(PSB) and phosphate-mineralizing bacteria(PMB),in some poplar plantations and to select potential microbial inoculants that could increase the P uptake by plants.Seventy four PSB strains and 138 PMB strains were preliminarily screened from 797 colonies isolated from the rhizosphere soil of poplar by the visible decolorization in the National Botanical Research Institute’s phosphate growth medium(NBRIP) containing a pH indicator of bromophenol and by the clear/halo zone on yeast malt agar plate,respectively.Then,based on the solubilization of Ca 3(PO 4) 2 in liquid NBRIP medium and the mineralization of lecithin in liquid Menkina medium,15 PSB strains and 7 PMB strains were further determined for their abilities to solubilize Ca 3(PO 4) 2 and to mineralize lecithin.The results showed that the 15 PSB strains exhibited inorganic P-solubilizing abilities ranging between 376.62 and 669.56 mg L -1 and the 7 PMB strains exhibited organic P-mineralizing abilities varying from 0.32 to 1.56 mg L -1 three days after incubation.Three of PSB strains with the highest P-solubilizing ability,named JW-JS1,JW-JS2 and JW-SX2,were all preliminarily identified as Pseudomonas fluorescens,while two of PMB strains with the highest P-mineralizing ability,named JYZ-SD1 and JYT-JS2,were preliminarily identified as Bacillus cereus and Bacillus subtilis,respectively.All the efficient PSB and PMB strains should be further studied under both pot culture and field conditions to test their beneficial effects on poplar.     

Mathematical equations describing the behaviour of soil bacteria

A.D. McLaren made a major contribution to the development of quantitative studies in soil microbiology by presenting equations to describe the behaviour of microorganisms in soil. His three most important equations describe: the effect of the molecular environment at a solid-liquid interface on microbial activity; the vectorial reactions of nitrogen in soil; and the competition between species in soil. In his earlier research he illuminated physico-chemical features of the microenvironment of soil bacteria by means of kinetic models. Later his research expanded into the dynamics of microbial reactions in soil profiles and resulted in his second and third equations. Various experiments were carried to test these equations. Thus an elegant combination of the theoretical and practical aspects of soil microbiology was created. Furthermore he gave an insight into future research in modifying these classic approaches to include discrete and separate microsites.By studying bacterial populations established in capillary tubes inserted in soil, we have shown that there is a probabilistic feature in the proliferation of bacteria at microsites in soil: among several hundred viable bacteria existing at the start of the experiment only one or few bacteria proliferated during incubation. Colony formation of bacterial cells on solid media was described mathematically and this suggested that bacteria, after a lag, may form colonies by chance. The probability of forming colonies in a unit of time will depend on a large number of factors and vary according to species.     

Phosphate solubilizing microorganisms isolated from rhizosphere of maize cultivated in an oxisol of the Brazilian Cerrado Biome

Many soil microorganisms are able to transform insoluble forms of phosphorus to an accessible soluble form, contributing to plant nutrition as plant growth-promoting microorganisms (PGPM). The objective of this work was to isolate, screen and evaluate the phosphate solubilization activity of microorganisms in maize rhizosphere soil to manage soil microbial communities and to select potential microbial inoculants. Forty-five of the best isolates from 371 colonies were isolated from rhizosphere soil of maize grown in an oxisol of the Cerrado Biome with P deficiency. These microorganisms were selected based on the solubilization efficiency of inorganic and organic phosphate sources in a modified Pikovskaya's liquid medium culture containing sodium phytate (phytic acid), soybean lecithin, aluminum phosphate (AlPO₄), and tricalcium phosphate (Ca₃(PO₄)₂). The isolates were identified based on nucleotide sequence data from the 16S ribosomal DNA (rDNA) for bacteria and actinobacteria and internal transcribed spacer (ITS) rDNA for fungi. Bacteria produced the greatest solubilization in medium containing tricalcium phosphate. Strains B17 and B5, identified as Bacillus sp. and Burkholderia sp., respectively, were the most effective, mobilizing 67% and 58.5% of the total P (Ca₃(PO₄)₂) after 10 days, and were isolated from the rhizosphere of the P efficient L3 maize genotype, under P stress. The fungal population was the most effective in solubilizing P sources of aluminum, phytate, and lecithin. A greater diversity of P-solubilizing microorganisms was observed in the rhizosphere of the P efficient maize genotypes suggesting that the P efficiency in these cultivars may be related to the potential to enhance microbial interactions of P-solubilizing microorganisms.     

Entanglement of monofilament fishing lines and coral death

This study examined the extent of damage by monofilament fishing lines on the cauliflower coral (Pocillopora meandrina) colonies at a popular cast fishing site in Oahu, Hawaii in March 1998. Sixty-five percent of coral colonies had fishing lines on their surface, and 80% of colonies were either entirely or partially dead. The percentage of entirely and partially dead colonies was positively correlated with the percentage of colonies entangled with fishing lines. Percent dead coral surface area was larger for colonies with fishing lines than colonies without fishing lines. In colonies with fishing lines, percent dead coral surface area was positively correlated with percent area with fishing lines. The high incidence of coral colonies with fishing lines and the three sets of significant results indicated destructive effects of monofilament fishing lines to P. meandrina corals. There is thus a clear case that reefs should be protected not only from the effects of excessive removal of fishes, but also from the effects of unsuccessful fishing that results in fishing-line entanglement on corals.     

Einfluß polychlorierter Biphenyle auf die mikrobielle Aktivität in Böden

Effects of polychlorinated biphenyls on soil microbial activity In laboratory experiments the microbial toxicity of the PCB congeners 5 (2, 3-Dichlorobiphenyl), 8 (2, 4′-Dichlorobiphenyl), 29 (2. 4, 5-Trichlorobiphenyl) and 77 (3, 3′, 4, 4′-Tetrachlorobiphenyl) which is supposed to be extremely toxic to wildlife was investigated using Parabrownearth-Ap and Podsol-Ahe horizon material. In addition the technical PCB mixtures Arochlor 1242 and 1260 were tested. Microbial toxicity was measured by means of long-term respiration (CO₂-evolution), short-term respiration (CO₂-evolution 12 h, after addition of glucose), and dehydrogenase activity (TTC reduction) tests. 1 mg/kg of the Dichlorobiphenyls 5 and 8 reduced the long-term and short-term respiration of the Podsol-Ahe during the whole experiment (35 and 28 days, respectively). The Trichlorobiphenyl 29 became effective after addition of 10 mg/kg. No effect except a short stimulation of long-term respiration was observed for PCB 77 (Tetrachloro-PCB). Due to its higher sorption capacity, all PCB congeners reduced the microbial activity of the Parabrownearth-Ap to a lower degree. In general the toxicity of PCBs decreased with increasing degree of chlorination in both soil horizons. The technical mixtures reduced the long-term respiration only after high additions of 50 mg/kg (Podsol-Ahe) and 100 mg/kg (Parabrownearth-Ap), respectively. Arochlor 1242 proved to be more toxic than Arochlor 1260.