Copper, phytotoxic

There are instances, for example with aluminum and copper, where even phytotoxic concentrations pose no health hazard to animals (143). Lead contamination, on the other hand, is considered a bigger hazard to man and animal by accidental ingestion than to plants because it is largely unavailable (insoluble) to the latter (100). Fortunately, the element is largely removed by simple rinsing (144). Fluoride, in contrast to lead, is absorbed readily in the free form and tends to be phytotoxic at extremely low concentrations (145). 

Since the era of the antibiotics, no new compounds have been developed for the control of diseases caused by phytopathogenic prokaryotes. Even these antibiotics are not used in many areas of the world because of governmental restrictions that prevent their use on agricultural crops. Problems with resistance are reducing the usefulness of the antibiotics even further. Copper compounds, which are generally less effective than the antibiotics, are the main compounds available to control bacterial incited diseases. Unfortunately, copper compounds are phytotoxic to many crops. 

Phytotoxic effects attributed to high concentrations of arsenic have also been reported around the Mina Turmalina copper mine in the Andes, northeast of Chiclayo, Peru (Bech et al., 1997). The main ore minerals involved are chalcopyrite, FeAsS, and pyrite. Arsenic-contaminated ground-water in the Zimapan Valley, Mexico has also been attributed to interaction with Ag-Pb-Zn, carbonate-hosted mineralization (Armienta et al., 1997). Arsenopyrite, FeAs04-2H20, and (Cu,Fe)i2As4Si3 were identified as probable source minerals in this area. 

Ali NA, Ater M, Sunahara GI, et al. Phytotoxicity and bioaccumulation of copper and chromium using barley (Hordeum vulgare L.) in spiked artificial and natural forest soils. Ecotoxicol Environ Sa/2004 57(3) 363-74. 

Mathur, S. P. and Levesque, M. P. (1983a). The effects of using copper for mitigating Histosol subsidence on 11. The distribution of Cu, Mn, Zn, and Fe in an organic soil, mineral sublayers and their mixtures in the context of setting a threshold of phytotoxic soil-Cu. Soil Sci. 135, 166-176. 

Fertile soils supply plants with all of the trace elements essential for growth, believed at the present time to be Fe, Mn, Zn, B, Cu, Mo, and CL These seven elements are called the micronutrients, a term that indicates the small quantities needed by plants but not necessarily the concentrations found in soils. Deficiencies can occur in soils either because they contain extremely low concentrations of these elements or because the elements are present in very unavailable (insoluble) forms. Conversely, many trace elements, including ail of the micronutrients, can reach concentrations in soils that are toxic to plants and microoiganisms. Some of the most toxic are mercury (Hg), lead (Pb), cadmium (Cd), copper (Cu), nickel (Ni), and cobalt (Co). The first three are particularly toxic to higher animals. The last three are more toxic to plants than animals and are termed phytotoxic. From the standpoint of potential hazard to human health, an extended Ust of priority metals has been established. This list presently consists of ... 

Toxicity of natural origin is found in soils formed from Cu sulfide-rich parent rocks, especially when the soil is acid. Bioaccumulation of Cu in humus followed by episodes of reduction can concentrate the element in sulfide form in natural wetlands. Because copper is not only phytotoxic but also a commonly abundant metal pollutant in waste materials, Cu in wastes such as sewage sludges is often the first element to limit land application. 

Water-soluble copper compounds can also exert phytotoxic effects, hence the... 

Water-soluble copper compounds are in any case unsuitable as foliage sprays, due to their strong scorching effect. The phytotoxity of water-insoluble copper compounds is weaker, and is to be expected when more soluble copper compounds are formed than needed. Phytotoxicity is caused by the copper(ll) ions penetrating the plant cells. Fortunately, the translocation of copper(II) ions is moderate in plants, so that only local damage occurs and the whole plant is not killed. 

To avoid the difficulties of preparation, several dry preparations have been put on the market, from which a spray can be simply prepared with water. A stable product of high activity that is less phytotoxic and is resistant to weather is formed by dehydrating the 10% aqueous suspension of copper sulfate and calcium hydroxide with a stream of hot air at 80-175°C (Hess et al., 1968). 

The active substance of Burgundy mixture is also basic copper(II) carbonate. Owing to difficulties in the preparation of Bordeaux mixture, Masson (1887) recommended the use of soda instead of lime. The use of Burgundy mixture increased after the World War I. Its tenacity, however, is inferior to that of Bordeaux mixture and its phytotoxic effect greater. 

Copper(I) oxide (CU2O) is a reddish crystalline powder, practically insoluble in water. Its protectiveness against bunt depends on weather and other conditions, so it has not been widely used. It is not phytotoxic, so it was also used for a time as a spray against Phytophtora and Peronospora spp. Its acute oral lDj for rats is 470 mg/kg (Horsfall, 1932). 

Organic tin compounds are contact fungicides. Their range of action is similar to that of copper compounds, but they are considerably more potent. However, their use for plant protection is limited by their phytotoxicity to more sensitive plants, and by their strong and lasting toxic action on warm-blooded organisms. Recent research has been concerned mainly with the reduction of both of these harmful effects. 

Wang, R, D. Zhou, T.B. Kinraide, et al. 2008. Cell membrane surface potential (psiO) plays a dominantrole in the phytotoxicity of copper and arsenate. Plant Physiol. 148 2134—2143. Wang, P., D.M. Zhou, L.Z. Li, et al. 2010. Evaluating the biotic ligand model for toxicity and the alleviation of toxicity in terms of cell membrane surface potential. Environ. Toxicol. Chem. 29 1503-1511. 

These are largely compounds of sulphur, copper and mercury. Elemental sulphur is probably the oldest effective fungicide known and was recommended as early as the beginning of the nineteenth century to control mildew on fruit trees. The use of Bordeaux mixture on vines has already been mentioned. Other (simple) copper salts (e.g. copper sulphate, cuprous oxide) have also been used as fungicides. Problems with phytotoxicity have led to their replacement by the more effective modern fungicides. 

Bradshaw [256] has suggested that sowing derelict land, heavily contaminated with copper, lead, tin and zinc, with tolerant plant strains offers the best possiblity of reclamation. It should be borne in mind, however, that it may be euphemistic to describe areas as having been reclaimed which are inhabited by populations of plants which may contain levels of potentially toxic metals substantially in excess of normal phytotoxic limits. The occurence of phyto-... 

Now that we are armed with some information on the available levels of common contaminant elements associated with contamination of soils in urban and industrial areas, the levels of elements in plants grown on contaminated soils and the threshold phytotoxic levels for a number of different kinds of plant, it should be possible to do rather better than speculate about the possible long-term consequences of the dispersion of trace elements in the environment. It is already obvious that the ability of plants to restrict their intake of a number of metals, notably copper, lead and mercury, has protected us from serious nutritional problems arising from the marked degree of contamination of soils with these elements which has already occurred within our towns and cities. Unfortunately, this natural barrier does not always protect infant children reared in the urban environment, for some of them directly ingest appreciable quantities of soil in which the levels of these elements are markedly enhanced as a result of contamination. 

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