Plants, terrestrial arsenic

Arsenic may be taken up by estuarine as well as terrestrial plants. Usually arsenate is preferred compared to arsenite in view to plant uptake (Aller et al., 1990). Table 2 presents the total arsenic content of some vegetables. 

Lethal and sublethal effects of various arsenic compounds on selected species of terrestrial plants and invertebrates... 

Marine algae transform arsenate into nonvolatile methylated arsenic compounds such as methanearsonic and dimethylarsinic acids (Tamaki and Frankenberger 1992). Freshwater algae and macrophytes, like marine algae, synthesize lipid-soluble arsenic compounds and do not produce volatile methylarsines. Terrestrial plants preferentially accumulate arsenate over arsenite by a factor of about 4. Phosphate inhibits arsenate uptake by plants, but not the reverse. The mode of toxicity of arsenate in plants is to partially block protein synthesis and interfere with protein phosphorylation — a process that is prevented by phosphate (Tamaki and Frankenberger 1992). 

Although arsenic is not an essential plant nutrient, small yield increases have sometimes been observed at low soil arsenic levels, especially for tolerant crops such as potatoes, com, rye, and wheat (Woolson 1975). Arsenic phytotoxicity of soils is reduced with increasing lime, organic matter, iron, zinc, and phosphates (NRCC 1978). In most soil systems, the chemistry of As becomes the chemistry of arsenate the estimated half-time of arsenic in soils is about 6.5 years, although losses of 60% in 3 years and 67% in 7 years have been reported (Woolson 1975). Additional research is warranted on the role of arsenic in crop production, and in nutrition, with special reference to essentiality for aquatic and terrestrial wildlife. 

Table 28.3 (continued) Lethal and Sublethal Effects of Various Arsenic Compounds on Selected Species of Terrestrial Plants and Invertebrates... 

Most bore waters include high concentrations of at least one of the following chemical contaminants (Table 1) lithium (Li), boron (B as H3BO3), arsenic (As), hydrogen sulphide (H2S), mercury (Hg), and sometimes ammonia (NH3). If released into a river or lake, these contaminants can potentially damage aquatic life, terrestrial plants, and/or human health. The disposal of highly saline bore waters can also have an adverse effect on water quality. 

As mentioned in Section II, arsenate is present in seawater at a fairly uniform concentration (about 0.5-2 ng As/liter), and in nutrient-deficient waters its concentrations may exceed that of the essential phosphate (146). In oxygenated seawater, the species exist predominantly as H2PO4 and H2As04, and algae may absorb arsenate because it is similar to the phosphate anion (147). In terrestrial plants and other organisms, arsenic is taken up by the phosphate transport mechanism... 

NOM is common in sediments, soils, and near ambient (<50 °C) water. The materials result from the partial decomposition of organisms. They contain a wide variety of organic compounds, including carboxylic acids, carbohydrates, phenols, amino acids, and humic substances (Drever, 1997, 107-119 Wang and Mulligan, 2006, 202). Humic substances are especially important in interacting with arsenic. They result from the partial microbial decomposition of aquatic and terrestrial plants. The major components of humic substances are humin, humic acids, and fulvic acids. By definition, humin is insoluble in water. While fulvic acids are water-soluble under all pH conditions, humic acids are only soluble in water at pH >2 (Drever, 1997, 113-114). 

Humans and wildlife are exposed to arsenic from mining wastes through food, water, and air (Chapter 4). Arsenic in mine drainage and other waters may also enter plants and aquatic animals. Terrestrial... 

Quaghebeur, M., Rengel, Z., Smirk, M. Arsenic speciation in terrestrial plant material using microwave-assisted extraction, ion chromatography and inductively coupled plasma mass spectrometry. J. Anal. At. Spectrom. 18, 128-134 (2003)... 

Pitten, F.A., Muller, G., Konig, P., Schmidt, D., Thurow, K., Kramer, A. (1999). Risk assessment of a former military base contaminated with organo-arsenic-based warfare agents uptake of arsenic by terrestrial plants. Sci. Total Environ. 226 237 5. 

The term hyperaccumulators was first used by Brooks et al. [113] to describe the plants that take up and accumulate more than 1000 pmoles As/g dry weight. A report about an arsenic-hyperaccumulating fern species additionally discussed the ph)Poremediation potentials of such plants [114]. Recent investigation has shown that the arsenic compounds in terrestrial and aquatic plants, fimgi, and lichen species are also interesting natural products [115, 116]. 

All manner of pollutants are considered under the discipline of terrestrial ecotoxicology including pesticides, persistent organic pollutants, other organic substances, and metals and metalloids (e.g., selenium and arsenic). Naturally occurring toxins such as those produced by poisonous plants, snakes, or invertebrates generally are not included unless people intentionally apply them for pest control. For example, the pyrethroid pesticides are derived from the naturally occurring pyrethrin toxin that is found in chrysanthemum. 

Terrestrial and Marine Flora and Fauna Arsenic contents in most plants, or parts of them grown on noncontaminated soils, are relatively low and normally vary from 3pgkg to about 1.2mgkg (Michels... 

A number of terrestrial plants are known not only to tolerate but also to hyperaccumu-late metals, and thus they might be useful for phytoextraction. Recently, a brake fern Pteris vitata) was identified that not only can tolerate up to 1500 mgkg arsenic in soil, but has also a bioconcentration factor of about 190 that leads to a content of 2.3% (dry weight), mainly as As " and As (Zhang et al. 2002). 

Suitable methods for speciation analysis of phenylarsenic compounds in soil and plant samples have been developed. In spite of the considerable contamination of the soil, the arsenic content of terrestrial plants is apparently modest. 

D Kuehnelt, J Lintschinger, W Goessler. Arsenic compounds in terrestrial organisms IV Green plants and lichens from an old arsenic smelter site in Austria. Appl Or-ganomet Chem 14 411-420, 2000. 

Arsenate and arsenite are major forms of arsenic in freshwater and terrestrial plants. 

Tetramethylarsonium ion is a common arsenic species in marine animals. It is present usually as a minor constituent, although exceptions do occur for example, it is a significant arsenical in several species of bivalve mollusks (1). Traces of tetramethylarsonium ion have been found in some freshwater animals (6). It has also been reported in several fungal species, usually at low levels, and as a trace constiment of some terrestrial plants as well (6). There have been no reports of tetramethylarsonium ion in seawater or freshwater. 

Trimethylarsine oxide has been reported in several marine animals, where it is almost always a trace constituent. The one exception is the fish Kyphosus sydney-anus, which has trimethylarsine oxide as the major arsenical (25). That trimethylarsine oxide is not more widespread is perhaps surprising since it is likely to be a metabolite of the same pathway producing methylarsonate and dimethylarsinate, both of which are more commonly found. Trimethylarsine oxide chromatographs rather poorly on cation-exchange columns often used for determining arsenic species, and the resultant poor detection limits for this compound may partly explain the data indicating its apparent absence in many samples. Trimethylarsine oxide is usually only rarely reported in terrestrial organisms, but more recent work (with better detection limits) has shown it to be present in various terrestrial plants and two lichen samples (26). 

The arsenic chemistry of terrestrial plants is dominated by inorganic arsenic. With few exceptions, all plant species examined so far contain either arsenite or, more usually, arsenate as their major arsenical. Methylarsonate and dimethylarsinate are also commonly found. 

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