Toxic Heavy Metals

Types of contaminants

Contaminants include excessive levels of plant nutrients, introduced pathogenic organisms, heavy metals, and residues of prohibited substances. Heavy metals. Arsenic is added to broiler poultry feed to reduce diseases and stimulate growth. This heavy metal passes through the birds and is deposited in the poultry litter, thereby contaminating this source of plant nutrients. Litter from layer operations may contain copper or zinc that leaches from the cages. Composts may include residues of plants that were treated with pesticides containing heavy metals. Additionally, fertilizer pellets made from manure or litter may have additives that contain heavy metals or other non-allowed substances.

Environmental stresses

Having dealt with the processes occurring in the natural habitat and in horticulture, it remains to mention some of the factors working against a diverse habitat. The main stresses to ecosystems in Britain and other parts of Western Europe are acidity, excess nutrients, high water tables and heavy metals.

Manuring and Composting

This has created some concerns in the organic community, since much manure is now generated by large, industrial agriculture feeding operations called CAFOs (Confined Animal Feeding Operations). Not only are there concerns about contaminants (heavy metals, antibiotics, pesticides, hormones) but many in the organic community also object to any partnering with this segment of conventional agriculture, which is considered at odds with the environmental and social values represented by organic farming.

Agricultural Use Of Sewage Sludge

Problems associated with the agricultural use of sewage sludge include groundwater, soil and crop contamination with pathogens, heavy metals, nitrates, and toxic and carcinogenic organic compounds.34 Sewage sludge is a lot more than organic agricultural material. It can contain DDT, PCBs, mercury and other heavy met-als.35 One scientist alleges that more than 20 million gallons of used motor oil are dumped into sewers every year in the United States.36 grown on the plot for heavy metals. On finding that the heavy metals (lead, copper, nickel, zinc and cadmium) had been taken up by the plants, he concluded, Contamination of soils with a wide range of potentially toxic metals following application of sewage sludge is therefore virtually irreversible. 39 In other words, the heavy metals don't wash out of the soil, they enter the food chain, and may contaminate not only crops, but also grazing animals.40 Other studies have shown that heavy metals accumulate in the vegetable tissue of the...

Two Cell Constructed Subsurface Flow Wetland For Graywater Or Blackwater

Subsurface Constructed Flow Wetland

Aquatic plants can take up and sometimes metabolize water contaminants such as insecticides and benzene. The water hyacinth, for example, can remove phenols, algae, fecal col-iforms, suspended particles and heavy metals including lead, mercury, silver, nickel, cobalt and cadmium from contaminated water. In the absence of heavy metals or toxins, water hyacinths can be harvested as a high-protein livestock feed. They can also be harvested as a feedstock for methane production. Reed-based wetlands can remove a wide range of toxic organic pollutants.19 Duckweeds also remove organic and inorganic contaminants from water, especially nitrogen and phosphorous.20

Testing on your own or sending a sample to the tab

You can also send a soil sample to a lab for testing. The nutrient level and pH test results are more accurate and detailed than those provided by home kits. In addition, testing labs can look for things that home kits can't, such as organic matter and micronutrients, as well as heavy metals and other industrial residues. (Soils near heavily traveled roads or on old industrial sites can contain chemicals and metals that you may want to know about before planting a vegetable garden.)

Fertilizers Once Marketed

Another interesting study published in 1989 indicated that bacteria surviving in sewage sludge show a high level of resistance to antibiotics, especially penicillin. Because heavy metals are concentrated in sludge during the treatment process, the bacteria that survive in the sludge can obviously resist heavy metal poisoning. These same bacteria also show an inexplicable resistance to antibiotics, suggesting that somehow the resistance of the two environmental factors are related in the bacterial strains that survive. The implication is that sewage sludge selectively breeds antibiotic-resistant bacteria, which may enter the food chain if the agricultural use of the sludge becomes widespread. The results of the study indicated that more knowledge of antibiotic-resistant bacteria in sewage sludge should be acquired before sludge is disposed of on land.48 nitrates and heavy metals that are present in the sludge. They point out that the need to find ways to get rid of sludge is compounded...

The effects of specific abiotic factors pollutants on plants

Penny Covered Table Top

Heavy metals may be released into the air or into rivers as by-products of chemical industries and the burning of fossil fuels. Cadmium, lead and mercury are three commonly discharged elements. While plants are more tolerant of these substances than animals, there is a slow increase within the plant cells, and more importantly the levels of chemicals increase dramatically as the plants are eaten and the chemicals move up the food chains (see also DDT p58). There is constant monitoring by Government agencies for the factors mentioned above. This is especially so in National Parks, National Nature Reserves (NNRs), and Sites of Special Scientific Interest (SSSIs). Environmental scientists and laboratories have a range of techniques for assessing levels of these factors. Chemical tests for common nutrient substances and for pH can be performed in the field. More sophisticated analysis is required for heavy metals and pesticides. A common five day test for water quality called 'Biological...

Alternative Wastewater Treatment Systems

New systems are being developed to purify wastewater. One popular experimental system today is the constructed, or artificial wetlands system, which diverts wastewater through an aquatic environment consisting of aquatic plants such as water hyacinths, bullrush-es, duckweed, lilies and cattails. The plants act as marsh filters, and the microbes which thrive on their roots break down nitrogen and phosphorous compounds, as well as toxic chemicals. Although they don't break down heavy metals, the plants absorb them and they can then be harvested for incineration or landfilled.31

Wooden performance

One problem with wooden bins is cost. Wooden bins are not inherently more expensive than the plastic ones, but they are rarely available free or at subsidized prices. A new wooden bin can work out quite expensive even if you buy wood to make your own. Untreated, sawn (that is, not planed) timber is cheapest. Treated wood will last much longer, but seriously green gardeners should enquire what is in the wood preservative, since some contain heavy metals or other toxic chemicals.


In greenhouse vegetable production composted manure is often used as fertiliser. As organic farms and greenhouse production are not always closely located, transport of the manure can be an expensive and laborious process. As growing media for ornamentals, different types of composted waste have also been proposed, but these are not suitable as peat substitutes as they are too compact and often have a high content of nutrient salts and heavy metals (Weinhold and Scharpf, 1997). Alternatively, replacement of the animal manures in favour of easily available composted plant residues could be a more sustainable solution. Nutrient rich plant material such as clover could be grown in the field close to the greenhouse productions, and residues from other field productions such as different straw materials could be used. Compost based on plant residues must contain at least two different plant material types nutrient poor materials such as straw as structural component, and nutrient rich...