Metals, toxic absorption

Metal Toxic Effects person) Source of Exposure Absorption... 

The physiological role of metallothioneins remains unknown, but it may be, in part, to protect cells from metal toxicity by binding metal ions. Metallothioneins may also be important for intestinal and renal absorption of metals and for metal storage and excretion. 

Markich SJ and Jeeeree RA (1994) Absorption of divalent trace metals as analogs of calcium by Australian freshwater bivalves an explanation of how water hardness reduces metal toxicity. Aquat Toxicol 29 257-290. 

From these results it was concluded that neonatal age is a period of greatly increased metal absorption different organ distribution different metal-metal interaction and higher acute oral metal toxicity. It therefore seems reasonable to consider the early neonatal age as a critical period for metal accumulation and therefore of metal toxicity. 

Nubient deficiencies can enhance metal toxicity. For example low dietary calcium, zinc, and iron enhance the absorption and toxicity of lead. 

Toxicity. Inorganic mercury compounds, aryl mercury compounds, and alkoxy mercurials are generahy considered to be quite similar in their toxicity. Alkyl mercury compounds are considered to be substantiahy more toxic and hazardous. Mercury and its compounds can be absorbed by ingestion, absorption through the skin, or by inhalation of the vapor. The metal itself, however, rarely produces any harmful effects when ingested (16). 

Toxicology. Inorganic tin and its compounds are generally of a low order of toxicity, largely because of the poor absorption and rapid excretion from the tissues of the metal (42—49). The acidity and alkalinity of their solutions make assessment of their parenteral toxicity difficult. The oral LD q values for selected inorganic tin compounds are Hsted in Table 2. It is estimated that the average U.S. daily intake of tin, which is mostly from processed foods, is 4 mg (see Food processing). 

The pH of rainwater is normally about 6 but can be reduced significantly by absorption of acidic exhaust gases from power stations, industrial combustion or other processes, and vehicles. Acids may also enter the waterways as a component of industrial effluent. In addition to the direct adverse effects on aquatic systems (Table 16.12) low pH can result in the leaching of toxic metals from land, etc. 

Recycling of printer circuit boards is deemed as the most important source of heavy metals to the ambient environment. These heavy metals may be entering into human body from various exposure routes such as ingestion, inhalation, and dermal absorption. Exposure to high levels of heavy metals can lead to acute and chronic toxicity, such as damage to central and peripheral nervous systems, blood composition, lungs, kidneys, liver, and even death [14],... 

Phytate (myo-inositol hexaphosphate Fig. 15.3, structure 33) is found in many food species and can be considered as a phytochemical. Its role in the plant is primarily as a phosphate store in seeds, but it is found in other tissues as well, for example, tubers (Harland et al., 2004). Phytate and its hydrolysis products are anti-nutrients that chelate metal ions and thus reduce their bioavailability (Persson et al., 1998 House, 1999). This is particularly a problem with cereal grains, but pre-processing can improve mineral absorption from these foods (Agte and Joshi, 1997). There is some concern that high phytate foods could also contain higher levels of toxic heavy metals caused by natural accumulation. Plants also contain phytate-degrading enzymes that can also influence metal ion bioavailability (Viveros et al., 2000). 

Bacteria and their composites with soil minerals or organic matter are capable of taking up a wide range and variety of toxic metals in soil environments. Research done over the last decade or so has greatly improved our understanding of the mechanisms on biosorption of metals and bacte-ria-metal-soil component interactions. However, more studies from molecular level are needed in order to enhance the ability of bacteria and their association with soil components to remediate toxic metals-contaminated soils. The focus of future investigations should be on the mechanisms by which metals are sorbed and bound by bacterial cell surfaces and bacteria-soil/mineral composites. In this connection, X-ray absorption spectroscopy (XAS) is a promising technique because it can provide information about... 

Statham [448] has optimised a procedure based on chelation with ammonium dithiocarbamate and diethylammonium diethyldithiocarbamate for the preconcentration and separation of dissolved manganese from seawater prior to determination by graphite furnace atomic absorption spectrometry. Freon TF was chosen as solvent because it appears to be much less toxic than other commonly used chlorinated solvents, it is virtually odourless, has a very low solubility in seawater, gives a rapid and complete phase separation, and is readily purified. The concentrations of analyte in the back-extracts are determined by graphite furnace atomic absorption spectrometry. This procedure concentrates the trace metals in the seawater by a factor of 67.3. 

Iron-, copper-, and zinc complexes of rutin, dihydroquercetin, and green tea epicatechins were found to be much more efficient inhibitors than parent flavonoids of toxic effects of chrysotile asbestos fibers on peritoneal macrophages and erythrocytes [168], It was proposed that in this case the enhanced activity of metal-flavonoid complexes was increased by the absorption on chrysotile fibers. 

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