Laman ini diujudkan buat anda yang mencari kaedah ubatan herba alam semulajadi untuk sakit barah, selain berkongsi pendapat dan pengalaman sesama ahli. Menyedari faktor penyebab barah selain mengelak penipuan kerana pesakit barah selalu ditipu oleh orang yang rakus mengaut untung semata-mata. Laman ini juga bertujuan menyingkap amalan buruk yang merugikan kita.
Ahad, 14 Oktober 2012
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Sam Angima Publish Date: Summer 2010 Vol No: Vol. V No. 3
In 2008, Dr. Dan Sullivan and I published
an OSU publication about heavy metals in garden and landscape soils due to many
questions of concern about this topic. Here I will summarize the main points in
this publication as it relates to farming. A heavy metal can be defined as a
chemical element with a specific gravity that is at least five times that of
water (considered one (1) at 39 oF for water). Specific gravity is a measure of
density of a given amount of a solid substance when it is compared to an equal
amount of water. Examples of heavy metals that fall into this category include
arsenic, cadmium, iron, lead, chromium, copper, zinc, nickel, and mercury.
Not all heavy metals are toxic to humans.
In small quantities, metals such as iron, copper, manganese, and zinc are
essential for good health. Heavy metals such as lead are also good industrial
ingredients e.g. used in car batteries. However, these heavy metals become
toxic when they do not get metabolized by the body and end up accumulating in
the soft tissues. Ingestion is the most common route of exposure to heavy
metals. In plants, uptake of heavy metals depends on the plant species and
bio-availability of the metal in the soils. Since most of the ingestion of
heavy metals occurs from consumption of plants, then addressing how plants
acquire heavy metals can aid in controlling heavy metal toxicity.
If you happen to ingest heavy metals, that
alone is not enough to cause toxicity. In laboratory animals, absorption of
toxic metals may occur as a result of chronic deficiencies of calcium and
magnesium in the body and in other cases, excess levels of aluminum mobilizes
calcium and heavy metals to move from bones to the central neural tissue. Of
the many heavy metals of concern, lead and arsenic have been found to be higher
than federally set levels in most soils studied (note that all heavy metals
exist naturally in the soils largely in complex forms with other minerals – see
Table 1, showing average abundance of total heavy metals in the earth’s crust
and in typical soils).
Arsenic is the most common cause of acute
heavy metal poisoning in adults (but the source is not from soils). Arsenic is
released into the environment by the smelting process of copper, zinc, and lead
and from manufacture of chemicals and glass. Lead on the other hand is the
leading cause of heavy metals poisoning with major source coming from soils.
Excess levels of lead in soils greater than 400 ppm result from prior use of
lead paint around houses, lead-arsenate sprays for pest control during
1910-1950s, use of leaded gasoline (up to 1996 in Oregon), locations close to
former smelters & tailings from metal ore mines, and proximity to fossil fuel-fired
electrical plants. Therefore the culprit to look for when looking at heavy
metals in soils is lead toxicity.
A local study on lead contaminated soils
was carried out in Multnomah County in 2001 around homes built before 1930.
They found that in bare soil play areas lead concentrations were often above
the EPA limit of 400 ppm. The main reason why lead is found in close proximity
to the loading point is because lead is held tightly on surfaces of very fine
clay and organic matter particles and therefore accumulates in the top 1-2
inches of soil unless disturbed by excavation and tillage. Therefore if you
think you might have lead contamination in your farm or home, the best
procedure to follow is to collect soil samples and have them analyzed for lead content.
OSU publications EM 8677 and EC 628 provide laboratories that can do heavy
metal soil testing and how to sample soil for home gardens and small acreages
for soil testing, respectively. If you are testing for farming purposes, always
take soil samples to tillable depth depending on how deep your current
equipment disturbs the soil.
Once you receive you soil test back, use
Table 2 to interpret what you need to do for your specific soil in question.
Soil tests showing less than 50 ppm lead, generally show no lead contamination
while those showing greater than 1,200 ppm lead, are not recommend for any
gardening practices, rather they should be mulched heavily and planted to
perennial plants that do not need harvesting of food for human consumption.
Other abatements in soils testing high in lead are to use container or raised
bed gardening with clean soils and installing a barrier (e.g. geotextile fiber)
between good soils and contaminated soil below.
If your soil tests for lead higher than 50
ppm, you might need to use some soil amendments to reduce lead toxicity. These
1. Maintaining a neutral soil pH above 6.5.
Lead up take by plants is reduced when pH is above 6.5.
2. Add phosphorus when soil tests indicate
a need. Phosphorus reacts with lead to form insoluble compounds, therefore
3. Add organic matter, (OM) which in turn
binds lead and makes it less soluble in soil water. When testing OM, soil pH
soil should be maintained above 6.5 to reduce uptake by plants.
4. What about lead in water? If you still
have leaded water pipes, you should test your water for lead content. It is
recommended to replace these pipes or keep water off edible plants. What about
lead in fertilizers? Most fertilizer and soil amendment products do not significantly
increase health risks. Fertilizer manufacturers are required to test products
for lead, and tell Oregon Department of Agriculture or Washington Department of
Agriculture. Check online for Oregonhttp://oregon.gov/ODA/PEST/fertilizer.shtml
and online for Washington,
http://agr.wa.gov/PestFert/Fertilizers/Metals.htm. Compost makers
and distributors are not considered fertilizers and
therefore are not required to provide lead analysis data to regulatory
agencies. However, many composters determine lead levels in their products and
will supply the analytical information to consumers upon request. Check out the
Winter 2010 issue of the Small Farm Newsletter for arsenic related toxicity
from treated lumber.
It is important to note that plants do not
absorb or accumulate substantial amounts of lead. Lead does not readily
accumulate in the fruiting part of vegetables and fruit crops (e.g. corn,
beans, squash, tomatoes, strawberries, and apples). Since lead is tightly bound
to clay particles, higher concentrations of lead will therefore be on surfaces
of leafy vegetables from lead laden dust (e.g. brassicas), and on surfaces of
root crops (e.g. carrots and potatoes) if soils are contaminated. Actually,
there is more concern about lead contamination from external lead on unwashed
produce than from actual uptake by plants. This raises the need for everyone to
always wash their produce before eating/cooking and places a big responsibility
on growers to always wash their leafy vegetables before marketing them since
lead laden dust can blow from distant places. Remember that soil contaminated
with lead looks and smells like normal soil. Lead does not biodegrade since it
has a half-life of about 53,000 years.