Heavy Metals

Neurotoxicity of Heavy Metals

Nearly all organ systems are affected in heavy metal toxicity, most commonly the nervous, gastrointestinal, hematopoietic, renal, and cardiovascular systems. To a lesser extent, lead toxicity involves the musculoskeletal and reproductive Heavy metals bind to sulfhydryl groups in proteins, resulting in alterations of enzymatic activity however, specific metals also have unique mechanisms of toxicity that may explain the variety of presentations (11). Encephalopathy is one of the leading causes of mortality in patients with heavy metal poisoning and is especially common in cases of lead poisoning. Neuropathies are also common, often presenting a challenge to diagnose and necessitating extended diagnostic studies (12).

Pollution versus contamination

In this chapter, pollution refers to a resource that has been contaminated beyond legal limits. Such limits are specifically designated by State agencies, but may be limited to only the water and air resources. However, limits can also be applied to soils and plants to prevent unsafe levels of heavy metals where municipal sludge is being applied. Fish and cattle (animal resources) may also be contaminated to unsafe levels with pesticides or other substances, but specific pollution limits for this resource may not be a part of State standards.

C Phosphate mineralization

Complexed (chelated) with soil organic matter and have very little potential to contaminate ground water supplies and aquifers. This immobilization is strongest in soils that have a high content of organic matter, pH greater than 6.0, and CEC of more than 5. However, application of organic waste containing high amounts of heavy metals can exceed the adsorptive capability of the soil and increase the potential for ground water or aquifer contamination. See chapter 6 for the impact of heavy metals on plants. Sandy soils that have low content of organic matter and low pH have a low potential for retention of heavy metals. These soils have the highest potential for heavy metals and trace element contamination of aquifers and ground water. Surface water contamination from heavy metals and trace elements is a potential hazard if agricultural wastes are applied to areas subject to a high rate of runoff or erosion.

Water source and treatment

There are few conclusive studies about the effects of water quality on the larval rearing of M. rosenbergii. The general issues of water quality are discussed in Chapter 13, but this chapter focuses mainly on the grow-out phase. New & Singholka (1985) and Valenti (1985) considered it essential to perform a complete chemical analysis of the water before choosing a hatchery water source. Both freshwater and seawater should be free from all kinds of pollution, such as heavy metals (from industrial sources), herbicide and insecticide residues (from agricultural sources), and biological contamination, indicated by the presence of faecal coliforms, which are common in residential and agricultural areas. For example, Law (1995) showed that the oil-spill dispersant Corexit 9527 found in Malaysian estuarine waters could inhibit the hatching of M. rosenbergii eggs. Tolerance levels for various substances are discussed in Chapter 13, but most of the research has been with juveniles rather than...

Neurotoxicity of Chemicals Commonly Used in Agriculture

Key words assessment, wild plants, rodenticides, heavy metals, organochlo-rides, organophosphates A multitude of chemical agents used in agriculture are known to have significant toxicity, many of them specifically developed to be toxic to animals. This chapter concentrates on the neurological consequences of occupational exposure to these and other common agents, including insecticides, pesticides, heavy metals, and volatile organic and plant toxins.

J Bioextraction of heavy metal contamination

Over time, previous land use techniques have left a legacy of soil and water contamination by herbicides, pesticides (including the very stable organo-chlorides such as DDT) and heavy metals such as arsenic, cadmium, lead and mercury. There are many examples where large areas of land, such as in Iowa and California in the USA, are severely damaged to the point that it is questionable whether farming should continue on such land. It should be remembered that if the soil is poisoned, the crops and livestock growing on that soil can be poisoned. If they are then used for human food, they can poison us as well, as we are at the top of the food chain.

Toxic Effects of Some Elements

Lead is tolerated at 1-5 mg kg-1 diet, but a sustained level of about 12 mg kg-1 would be lethal. Lead shot trapped in silage may partially dissolve in fermentation acids to give up to 3800 mg soluble Pb kg-1 DM. The daisy (Bellis perennis L.) can accumulate 60-80 mg Cd kg-1 from contaminated soils, which is 30 times more than grass, therefore herbage growing in the vicinity of derelict mine workings should be analysed for heavy metals. A 500-kg horse grazing rough terrain may ingest 1-2 kg of soil per day, so the amount of any industrial fallout, contamination or seepage should be deter-

Limitations And Potential

The option of last resort is to treat and dispose of the waste in safe landfills, while minimizing the resultant volume, since disposal sites are few and space is precious not to mention expensive. A given bioremediation technology should be able to perform on a large scale in order for it to be commercially viable. The organism or biomaterial selected to accomplish the goal of removing or altering a heavy metal or metal ion rendering it less toxic must be very efficient in performing its intended function. The literature is rich with reports of studies attesting to the potential of a particular biomass or biomaterial to carry out bioremediation of metal-contaminated waste streams, but few have actually ventured beyond the laboratory bench scale. What is clear is the apparent dearth of genetic engineering reports in the literature. Classical genetic selection methods have proven useful, for e.g., for isolating a strain of S. cerevisiae out of 240 tested, capable of uptake of 3.2 mg...

F Municipal and industrial sludge and wastewater application systems

Municipal sludge (and wastewater to a much smaller degree) contains heavy metals that can be detrimental to crops and human and livestock health. (See table 6-2 in chapter 6). The sludge needs to be analyzed for certain metals, such as mercury, lead, zinc, cadmium, and nickel. The annual application rate for cadmium is regulated. Specific cumulative applications for the life of the site have been established by the U.S. Environmental Protection Agency for all of these metals. The application rates are dependent on the soil characteristics. State regulations should be consulted for specific metal loadings.

Mycorrhizae And Bioremediation

In the mining process, not only plants are removed, but also upon soil replacement changes in texture and deposits of salts and heavy metals often result (Allen 1989). The toxicity of The mechanism that confers heavy metal tolerance in mycorrhizal fungi is largely unknown. The survival of AM and EM fungi in polluted soil may depend heavily on the density of the external hyphae. The absorption of heavy metals to the hyphal surface could reduce soil concentrations and thus accumulation of fungal and plant tissue (Denny and Wilkins 1987 Marschner and Dell 1994). Components of the fungal cell wall, such as chitin and melanin, can bind heavy metals to the extraradical mycelium (Denny and Wilkins 1987 Tam 1995). Turnau et al. (1996) found that the EM fungal mantle contained the highest levels of heavy metals while the Hartig net contained the lowest levels. Glomalin, the glycoprotein that coats AM fungal hyphae, could play an equally important role in protecting AM fungi and host plants...

Soilagricultural waste mineralization relationship

The mineralization of agricultural waste material is governed by the biological, chemical, and physical properties of soil and organic waste the soil moisture and the soil temperature. Organic waste mineralization is a process where microbes digest organic waste, reduce the waste material to inorganic constituents, and convert it to more stable organic materials. Inorganic materials released during this process are the essential plant nutrient (N, P, K), macronutrients and micronutrients, salts, and heavy metals.

Sludge Quality and Characteristics

The characteristics of stabilized or raw sludge that affect its suitability for land application and beneficial use include organic content, nutrients, pathogens, metals, and toxic organics. The fertilizer value of sludge, if evaluated and found to be suitable, is based mainly on the contents of nitrogen, phosphorus, and potassium. In food and agricultural wastewater treatment, sludge may not have sufficient phosphorus and potassium contents to provide good plant growth. Trace amounts of inorganic compounds in the sludge may spur or stunt growth of plants. Heavy metals in sludge, a perennial problem of municipal wastewater treatment plants, is less severe a problem in most food wastewater treatment processes. Detailed information regarding typical wastewater characteristics, including heavy metals, can be found in Metcalf and Eddy, Inc. (1991).

Advanced Wastewater Treatment Processes

Simplifiednitrogen Cycle Diagram

Biological treatment processes, in combination with primary sedimentation, typically remove 85 of the BOD5 and soluble solids originally present in the raw wastewater and some of the heavy metals. Activated sludge generally produces an effluent of slightly higher quality, in terms of these constituents, than trickling filters or RBCs. When coupled with a disinfection step, these processes can provide substantial but not complete removal of bacteria and virus. However, they remove very little phosphorus, nitrogen, nonbiodegradable organics, or dissolved minerals, and in an increasing number of cases this level of treatment has proved to be insufficient to protect the receiving waters from contaminations or to provide reusable water for industrial recycle. As a consequence, additional treatment steps have been added to wastewater treatment plants to provide for further organic and solids removals or to provide for removal of nutrients and or toxic materials. These postprimary and or...

Extracellular Precipitation of Metals

Exceeding a solubility product leads to precipitation of an insoluble salt of the reacting species. Sulfide anion (S22) and oxalate anion (C2O4_) are produced by some species of micro-organisms and these anions can form very insoluble salts with heavy metal ions which exhibit very small solubility products as noted by Veglio and Beolchini (1997). Copper phosphate precipitation occurring within the matrix of mycelia of the fungus Penicillium ochro-chloron after 4 days of incubation in shake flask cultures at pH 4, was demonstrated using scanning electron microscopy and energy dispersive x-ray microanalysis (Crusberg et al. 1994). Wrinkled 40-50 mm dia. spheres of insoluble copper phosphate, inferred from EDX analysis, are trapped within the mycelia of the fungus grown for 4 days in aerated cultures in the presence of 100mg l Cu2+. Penicilllium and Aspergillus have been shown to produce extracellular acid phosphatases which correlate with copper removal from solution (Haas et al. 1991...

Applicability of Biotechnology to Specific Agricultural Objectives

(i) Increasing Productivity and Stability of Crops in Rainfed and Marginal Environments. Producing more food on the same area of cultivated land would reduce pressure to expand cultivated areas to forests and marginal areas. Broadening tolerance of existing HYV cereals for drought, flooding, salinity, heavy metals, and other abiotic and biotic stresses would increase yields in rainfed areas. CIMMYT and IRRI, in cooperation with NARSs in different countries, are focusing their efforts to develop HYVs of rice and maize for rainfed areas.

CCationexchange capacity

Cation-exchange capacity (CEC) is an index of the soil's capacity to exchange cations with the soil solution. It affects the ability of the soil to adsorb and retain cations and heavy metals. Cations are held to the soil particles by adsorption and can be returned to the soil solution for plant use by the exchange process.

A Filtration

Soil filtering systems are used to deplete Biological Oxygen Demand (BOD), consume or remove such biostimulants as phosphates and nitrates, provide long term storage of heavy metals, and deactivate pathogens and pesticides. Soils suitable for use as filtering systems have permeability slow enough to allow adequate time for purification of water percolating through the soil system.

Natural seawater

Natural seawater supplies may originate either from the open sea or sometimes from shallow beach wells, where natural filtration helps to exclude harmful protozoa and bacteria. Usually, locations are chosen where the salinity is 30 to 35 p.p.t. Although estuarine water can be used, when its salinity is above 12 p.p.t., this source is normally avoided because the high level of micro-organisms, which require enhanced treatment before the water is used. Natural sea-water from shallowbeach wells wouldbe preferable (New& Singholka 1985) however, water analyses should be done to profile the chemical composition and detect any abnormalities or potential toxins (e.g. heavy metals, ammonia). The site requires careful choice to avoid pollution or low salinity during rainy seasons. Hsieh et al. (1989) reported lower M. rosenbergii postlarval production in Taiwan when polluted seawater was used in hatcheries.

G Trace elements

* The classification is based on the response of crops grown on acidic soils that have received a cumulative cadmium (Cd) application of 4.5 lb ac. It should not be implied that these higher uptake crops cannot be grown on soils of higher Cd concentrations. Such crops can be safely grown if the soil is maintained at pH of 6.5 or greater at the time of planting because the tendency of the crop to assimilate heavy metals is significantly reduced as the soil pH increases above 6.5.


The country recognizes the tremendous potential of improved crop plants containing genes that provide pesticidal properties, resistance to herbicides, tolerance to pests, diseases and stress (salt, heavy metals and drought), or combinations of these. Such improved plants are expected to reduce production costs. Once the issues of biosafety regulations and intellectual property have been settled, the country will be able to use such new plant technologies, which are now limited to only a few countries.


Biosorption is a term that describes the broad range of processes by which biomass removes metals (and other substances) from solution, yet it can also be used in a stricter sense to describe uptake by dead (detritus) or living biomass by purely physico-chemical processes such as adsorption or ion exchange (White et al. 1995). Metabolic processes inherent in living biomass may contribute to the uptake mechanism. Ideally a biosorbent has the ability to be recycled and the sorbed metal ions recovered for reuse or safer disposal. Choice of a suitable biotrap is at times made easier if certain genetic and biochemical characteristics of an organism are known. That fungi and yeast can serve as biotraps for heavy metals has been the subject of a great deal of research as evidenced by several prior reviews on the subject (Blackwell et al. 1995 Kapoor and Viraraghavan 1995 1997).

Distillery Waste

As can be seen, the values of BOD and COD may vary significantly and may reach extremely high values of over 300 and more than 150 g l, respectively. The pH ranges from 3 to 5. The waste can contain different amounts of solids up to more than 400 g l. For cultivating microorganisms, the content of carbon and nitrogen sources is the most important factor. The ratio of C N varies with the raw material used for alcoholic fermentation. In addition to the components given in Table 1, there are different amounts of organic and amino acids, polyols, vitamins, phenolics, etc. Minerals include potassium, phosphorus, sulfates, and some heavy metals. These components may also have an important influence on

Indoor nurseries

The general topic of water quality in grow-out systems is fully covered in Chapter 13 but some observations that are specifically relevant to nursery systems and the rearing of juveniles are included here. Mortalities, related to water quality in indoor nurseries, usually result from low dissolved oxygen and or high concentrations of nitrogenous compounds (Zimmermann & Sampaio 1998). Prawn PL are also extremely sensitive to contamination of tank water with toxicants such as arsenic in treated lumber, pesticides, hydrogen sulphide, and heavy metals such as copper and zinc (Coyle et al. 2003b). Further information on survival is contained in section 7.10 of this chapter.

N Sodium adsorption

Moderate (Low adsorption and exchange of cations, and heavy metals.) Reduce application rates. exchange of cations heavy metals.) Reduce application rates. (Increased availability of heavy metals and reduced plant growth potential.) Reduce application rates, apply lime, and incorporate. (Increased availability of heavy Heavy metals contaminants metals, reduced plant growth, can flow into ground water. and limited crop selection.) Reduce application rates, apply lime, and incorporate.

C Chemical reactions

Organic waste mineralization by-products consist of macro- and micro-plant nutrients, soluble salts, gases, and heavy metals. These by-products dissolve and enter soil water solutions as precipitation or irrigation water infiltrates the soil surface and percolates through the soil profile. The dissolved by-products are subject to the interactions of ionic exchange, adsorption, precipitation, or complexation. These processes store and exchange the macro- and micro-plant nutrient by-products of organic waste mineralization. They also intercept and attenuate heavy metals, salts, and other detrimental mineralization by-products that can adversely affect plant growth and crop production. Complexation is the interaction of metals with soil organic matter and some oxides and carbonates, resulting in the formation of large, stable molecules. This process extracts phosphorus and heavy metals from the soil solution. These stable complexes act as sinks for phosphorus, heavy metals, and some soil...