生物专业英语.docx

1、生物专业英语Assessing potential dietary toxicity of heavy metals in selected vegetables and food cropsAbstract: Heavy metals, such as cadmium, copper, lead, chromium and mercury, are important environmental pollutants, particularly in areas with high anthropogenic pressure. Their presence in the atmospher

2、e, soil and water, even in traces can cause serious problems to all organisms, and heavy metal bioaccumulation in the food chain especially can be highly dangerous to human health. Heavy metals enter the human body mainly through two routes namely: inhalation and ingestion, ingestion being the main

3、route of exposure to these elements in human population. Heavy metals intake by human populations through food chain has been reported in many countries. Soil threshold for heavy metal toxicity is an important factor affecting soil environmental capacity of heavy metal and determines heavy metal cum

4、ulative loading limits. For soil-plant system, heavy metal toxicity threshold is the highest permissible content in the soil (total or bioavailable concentration) that does not pose any phytotoxic effects or heavy metals in the edible parts of the crops does not exceed food hygiene standards. Factor

5、s affecting the thresholds of dietary toxicity of heavy metal in soil-crop system include: soil type which includes soil pH, organic matter content, clay mineral and other soil chemical and biochemical properties; and crop species or cultivars regulated by genetic basis for heavy metal transport and

6、 accumulation in plants. In addition, the interactions of soil-plant root-microbes play important roles in regulating heavy metal movement from soil to the edible parts of crops. Agronomic practices such as fertilizer and water managements as well as crop rotation system can affect bioavailability a

7、nd crop accumulation of heavy metals, thus influencing the thresholds for assessing dietary toxicity of heavy metals in the food chain. This paper reviews the phytotoxic effects and bioaccumulation of heavy metals in vegetables and food crops and assesses soil heavy metal thresholds for potential di

8、etary toxicity.Keywords: Heavy metals, Dietary toxicity, Vegetables, Food crops1. IntroductionRegulation, handling and bioremediation of hazardous materials require an assessment of the risk to some living species other than human being, or assessment of hazard to the entire ecosystem. Assessment en

9、dpoints are values of the ecosystem that are to be protected and are identified early in the analysis. Such endpoints may include life cycle stages of a species and reproductive or growth patterns. Ecosystem risk assessment is at its dawn with this area of environment sciences still requiring extens

10、ive work in the industrialized nations of the world for sustainability of the global ecosystem.Heavy metals, such as cadmium, copper, lead, chromium and mercury, are important environmental pollutants, particularly in areas with high anthropogenic pressure. Their presence in the atmosphere, soil and

11、 water, even in traces, can cause serious problems to all organisms. Heavy metal accumulation in soils is of concern in agricultural production due to the adverse effects on food quality (safety and marketability), crop growth (due to phytotoxicity) (Ma et al., 1994; Msaky and Calvert, 1990; Ferguss

12、on, 1990) and environmental health (soil flora/fauna and terrestrial animals). The mobilization of heavy metals into the biosphere by human activity has become an important process in the geochemical cycling of these metals. This is acutely evident in urban areas where various stationary and mobile

13、sources release large quantities of heavy metals into the atmosphere and soil, exceeding the natural emission rates (Nriagu, 1989; Bilos et al., 2001). Heavy metal bioaccumulation in the food chain can be especially highly dangerous to human health. These metals enter the human body mainly through t

14、wo routes namely: inhalation and ingestion, and with ingestion being the main route of exposure to these elements in human population. Heavy metals intake by human populations through the food chain has been reported in many countries with this problem receiving increasing attention from the public

15、as well as governmental agencies, particularly in developing countries.Vegetables constitute essential diet components by contributing protein, vitamins, iron, calcium and other nutrients, which are usually in short supply (Thompson and Kelly, 1990). They also act as buffering agents for acidic subs

16、tances produced during the digestion process. However, they contain both essential and toxic elements over a wide range of concentrations. Metal accumulation in vegetables may pose a direct threat to human health (Trkdogan et al., 2003; Damek-Poprawa and Sawicka-Kapusta, 2003). Chinese cabbage (Bras

17、sica chinensis L. cv. Zao-Shu 5), winter greens (B. rosularis var. Tsen et Lee cv. Shang-Hai-Qing), pakchoi (Brassica chinensis L.) and celery (Apiumg graveolens L. var. dulce DC) are some crops, which were assessed for heavy metal toxicity. Vegetables take up metals by absorbing them from contamina

18、ted soils, as well as from deposits on different parts of the vegetables exposed to the air from polluted environments (Zurera-Cosano et al., 1989). It has been reported that nearly half of the mean ingestion of lead, cadmium and mercury through food is due to plant origin (fruit, vegetables and cer

19、eals). Moreover, some population groups seem to be more exposed, especially vegetarians, since they absorb more frequently tolerable daily doses.Food contamination by heavy metals depends both on their mobility in the soil and their bioavailability. Though some of the mobility and bioavailability fa

20、ctors are easy to measure, determination of the food risk contamination is tricky. The aim of the present paper is to review concisely the phytotoxic effects and bioaccumulation of heavy metals in vegetables and food crops and assessment of soil heavy metal thresholds for potential dietary toxicity.

21、2. Hazardous Effects of Heavy Metals on Human HealthChronic low-level intakes of heavy metals have damaging effects on human beings and other animals, since there is no good mechanism for their elimination. Metals such as lead, mercury, cadmium and copper are cumulative poisons. These metals cause e

22、nvironmental hazards and are reported to be exceptionally toxic (Ellen et al., 1990). Vegetables take up metals by absorbing them from contaminated soils, as well as from deposits on parts of the vegetables exposed to the air from polluted environments (Zurera-Cosano et al., 1989).Metal contaminatio

23、n of garden soils may be widespread in urban areas due to past industrial activity and the use of fossil fuels (Chronopoulos et al., 1997; Snchez-Camazano et al., 1994; Sterrett et al., 1996; van Lune, 1987; Wong, 1996). Heavy metals may enter the human body through inhalation of dust, direct ingest

24、ion of soil, and consumption of food plants grown in metal-contaminated soil (Cambra et al., 1999; Dudka and Miller, 1999; Hawley, 1985). Potentially toxic metals are also present in commercially produced foodstuffs (DEFRA, 1999). Exposure to potentially toxic metals from dust inhalation or soil ing

25、estion is usually modelled simply as the concentration of a contaminant measured in the soil multiplied by the quantity of dust inhaled or soil ingested (Konz et al., 1989). This is a conservative approach to estimate dose, because the bioaccessibility of heavy metals adsorbed on ingested soil is no

26、t 100% (Ruby et al., 1999). However, predicting exposure to potentially toxic metals from consumption of food crops is more complicated because uptake of metals by plants depends on soil properties and plant physiologic factors. This leads to much larger uncertainties associated with estimating pote

27、ntial doses through food chains compared to the uncertainties associated with other exposure pathways such as soil ingestion and dust inhalation (McKone, 1994).Lead is a toxic element that can be harmful to plants, although plants usually show ability to accumulate large amounts of lead without visi

28、ble changes in their appearance or yield. In many plants, Pb accumulation can exceed several hundred times the threshold of maximum level permissible for human (Wierzbicka, 1995). The introduction of Pb into the food chain may affect human health, and thus, studies concerning Pb accumulation in vege

29、tables have increasing importance (Coutate, 1992). Although a maximum Pb limit for human health has been established for edible parts of crops (0.2 mg/kg) (Chinese Department of Preventive Medicine, 1994), soil Pb thresholds for producing safe vegetables are not available.Knowledge of Zn toxicity in

30、 humans is minimal. The most important information reported is its interference with Cu metabolism (Barone et al., 1998; Gyorffy and Chan, 1992). The symptoms that an acute oral Zn dose may provoke include: tachycardia, vascular shock, dyspeptic nausea, vomiting, diarrhea, pancreatictis and damage o

31、f hepatic parenchyma (Salgueiro et al., 2000). Although maximum Zn tolerance for human health has been established for edible parts of crops (20 mg/kg) (Chinese Department of Preventive Medicine, 1995), soil Zn threshold for producing safe vegetables is not available.According to Hough et al.(2004)

32、under Part IIA of the Environmental Protection Act 1990, the UK government favors a “suitable for use” approach to redevelopment (DETR, 2000): Land is contaminated only if the current or intended use of a site has the potential to cause an unacceptable health risk to human occupants or to the enviro

33、nment. Under the UK Town and Country Planning Act 1990 (DETR, 2000), this approach requires that land be assessed for redevelopment on a site-specific basis. At present, concentrations of metals in the soil are compared to metal-specific “trigger values” (termed “maximum contaminant levels” or “maximum contaminant concentrations” in North America). In the past these