Liming acid streams: Aluminium toxicity to fish in mixing zones

Liming to neutralize acidic surface waters involves a possible risk of toxicity to fish due to precipitation or changes in speciation of Al. We report the response of captive brown trout to the experimental liming of an acid stream rich in Al. Within 15 m of lime dosing 0.22 µm filterable Al fell from 580 to 230 µg L^?1, and to 120 jig L^?1, within 30 m, though total Al was unchanged. After 24 hr, fish mortality was 100% at untreated acidic sites, 80% up to 30 m downstream of liming, declining to zero within 100 m. Mortality was 70% at 15 m below the confluence of an acidic tributary with the limed stream, despite little change in pH or total Al concentration. Mortalities were significantly correlated with concentrations of Al and Fe in gill tissues, and with 0.22 µm filterable Al and Fe in the water, but not with particulate Al or Fe. AI(OH)₄ ^?, precipitating A1 or polymeric hydrolysis products are all possible causes of the observed toxicity. Iron may have also have contributed, but the stream concentrations of this metal were relatively low. The practical conclusion is that changes in Al chemistry, where waters of differing acidity mix, may be important in some circumstances where river systems are limed selectively.     

作物生产给植物提供真正所需

精准农业的目的就是要按照作物生长需要有针对性地进行栽培管理。该文从耕种方式、播种方式、施肥方式以及农田作业轨迹方面出发,介绍了现行一些精准农业发展情况,同时指出了所面临的问题及发展方向。      

A new arylnaphthalene lignan from Knema furfuracea

A new arylnaphthalene lignan, named furfuracin (1), was isolated from the leaves of Knema furfuracea (Myristicaceae), whereas 7 known compounds including (+)-trans-1,2-dihydrodehydroguaiaretic acid, fragransin A₂, biochanin A, gingkolic acid, anarcardic acid, 2-hydroxy-6-(12-phenyldodecyl)-benzoic acid and 2-hydroxy-6-(12-phenyldodecen-8′Z-yl)-benzoic acid were obtained from its stems. The structure of the new lignan was established by analysis of spectroscopic data (UV, IR, MS and NMR).     

A new 1,3-diketofriedelane triterpene from Salacia verrucosa

A new 1,3-diketofriedelane triterpene, 21α-hydroxyfriedelane-1,3-dione (1) together with six known friedelane triterpenes, 30-hydroxyfriedelane-1,3-dione (2), friedelane-1,3-dione (3), 26-hydroxyfriedelane-1,3-dione (4), friedelin (5), 21α-hydroxy-D:A-friedo-olean-3-one (6) and kokoonol (7), were isolated from the stems of Salacia verrucosa (Celastraceae). The structures of these triterpenes were characterized by spectroscopic methods (IR, MS and NMR). Compound 3 was strongly cytotoxic against SW620 cell line, whereas compounds 4 and 6 were moderately active against SW620, HepG2 and KATO-III cancer cell lines.     

Antioxidant lignan glucosides from Strychnos vanprukii

From the stem of Strychnos vanprukii, two new lignan glucosides, vanprukoside (1) and strychnoside (2), were isolated together with the known lignan glucoside, (+)-lyoniresinol-3 alpha-O-beta-glucopyranoside (3). The structures of these compounds were elucidated on the basis of their spectroscopic data. All three compounds exhibited antioxidant activity.