 |
CUSTOMER SUPPORT
CONTACT INFO |
Available
24 hours a day! |
|
 |
|
 |
|
THE ENVIRONMENTAL ADVANTAGES
OF USING DIFFUSIBLE PRESERVATIVES
William E. Currie Director, Int’l Pest Management Inst.,
Bryans Road, Maryland
Environmental
Advantages of Using Borates
The
environmental advantages of using diffusible preservatives, based upon boric
acid or its sodium salts, are considerable. These compounds have unique
characteristics of solubility, toxicity, volatility, durability and an ubiquitous
presence in soil, water and plants. Most borates occur in nature as several
closely related compounds, which differ mainly in their water of hydration
and are difficult to tell apart. Most are in the form of boric acid or boron
salts. Boron is a micronutrient in soil and borate salts occur naturally
in low concentrations in most unpolluted waterways. Risks to birds, fish
and wildlife species are minimal, although some common sense precautions
should be followed.
|
The use of diffusible borate materials
has been under consideration or in practice since the late 1930’s. Most
of the early work with diffusible borates was done in New Zealand and Australia.
Very little was done in the United States until the early 1960’s
When discussing the environmental advantages
of diffusible preservatives, "the environment" is described as that area
of the earth around us, the land, the water the air and the plants and animals
that occupy those areas; and the living and working environments inside
our buildings. The materials used to manage those pests that attack, damage
and destroy our commodities, structures, and peace of mind often may have
adverse effects on our health. .
Dietary exposure may occur when treated raw agricultural commodities
are eaten. Boron tolerances for residues were established at 30 parts per
million (ppm) in or on cotton seed and at 8 ppm in or on citrus fruits.
These tolerances covered pre- and post- harvest applications of boric acid,
borax, and other borates, plus the naturally occurring boron in agricultural
commodities. These tolerances indicate there is a low risk of human injury
from dietary exposure to the borates. Boron occurs naturally in fruits,
vegetable and forage crops and is an essential nutrient for plants. In pears
and strawberries, the natural levels may reach 160 ppm, and in red cabbage
occasionally go as high as 200 to 300 ppm. The increment of added boron
residues resulting from the use of boric acid or its salts is insignificant
compared to levels that naturally occur.
In 1993, the EPA established an exemption
from the requirement for a tolerance for residues of boric acid and its
sodium salts on all raw agricultural commodities (including cotton seed
and citrus) (5). Although there are no direct food application users, the
environmental presence of boron is much greater than what could occur from
its use as a diffusible wood preservative.
The EPA has also determined that boric
acid and its sodium salts do not show any evidence of carcinogenicity for
humans and no evidence of mutagenicity. However, boric acid and the borate
salts are lethal human poisons by ingestion at levels of 5 to 20 g. Exposure
through the skin, eyes, or inhalation is minimal, so minimal protective
measures are necessary. Expensive specialized protective gear is not needed.
Since 1934, borates have been known
to provide a good measure of fire retardancy to wood and paper. This can
provide an added environmental advantage by reducing fire risks within structures
from heat sources or even open flame for a short time. To achieve good fire
retardancy, higher levels of borate impregnation are needed than levels
that preserve wood from insect and fungi attack. Borate bombers using borate
solutions are still being used extensively to combat brush and forest fires.
Borates have a distinctive advantage
in that they are invisible when properly applied to wood or wood products.
This becomes especially important when preserving historic fabric found
in old homes, furniture, tools, or other artifacts. Historic buildings,
now under the care of the National Park Service or other historic preservation
societies, find that wood can be preserved indefinitely with borate solutions
without showing that a preservative has been used.
The borates are essentially nonvolatile.
This means that they do not evaporate ;from the site where applied. This
characteristic prevents environmental degradation from chemical trespass
from borate vapors. Additionally, indoor air quality is not adversely affected
by borate-preserved wood. This is also true for borates (boric acid or disodium
octaborate tetrahydrate (DOT)) used for management of cockroaches, fleas,
ants, silverfish, bed bugs, or other household insect pests. Most of the
other products available to the householder or professional cannot truthfully
make this claim.
With diffusible borate preservatives,
nonvolatile characteristics convey an additional bonus in being odorless.
Odorless borate-reserved wood used in home and furniture construction can
make a home more livable. Those with environmental illness or multiple chemical
sensitivity may not experience reactions to clean raw wood preserved with
a DOT solution.
|
Borates
are durable. They do not break down into ineffective byproducts.
They do not evaporate. Although they are water soluble, they do not move
far in the environment, especially in soil. If placed in solution, the
borates recrystallize and keep working when the water evaporates. When
properly applied for insect control in homes or other structures, their
insecticidal efficacy lasts for years and years. The same property of
durability applies to diffusible borates used for wood preservatives.
The borates have a relatively low toxicity
– LD-50 of about 3,500 mg per kg of body weight of test animals. There
are many other pesticide chemicals that have lower toxicity LD-50 ratings.
However, low toxicity does not necessarily equal low risk. Most pesticides
are volatile, which increases non-target risk. If all wood used in structures
or furniture was treated with diffusible borates, risks to people occupying
those structures would be greatly reduced.
Boron exists in four major forms in soil:
- in rocks and mineral;
- absorbed on surfaces of clays and hydrous iron
and aluminum oxides;
- combined with organic matter; and
- as free non-ionized boric acid (H3 BO3) and
B(OH)4 in the soil.
The
total concentration of boron
in soil varies between 2 and 200 ppm, most frequently ranging between 7
to 80 ppm. Boron is the only nonmetal among the micronutrient elements.
The boron complex in soil is bound to clay or organic matter to varying
degrees. However, this retards the movement of boron through the soil, reducing
its environmental impacts. In the soil, the boric acid is available to plants
that utilize its nutrient qualities. However, large amounts of boron can
inhibit growth and become toxic to plants.
The average concentration for born in
surface waters is reported to range from 0.001 mg/1 to 0.1
mg/1.
Seawater boron concentrations average 4.5 mg/l. the low toxicity
and ubiquitous natural occurrence reduce the potential risk to non-target
organisms. Boric acid and the borates are "practically nontoxic" to most
bird species. There are no records of field mortalities associated with
the use of boric acid. Although aquatic invertebrates are more sensitive
than fish, boric acid is considered "practically nontoxic" to fish and aquatic
invertebrates. The presence of boric acid and borates in the environment
provides an additional advantage to their use as wood preservative. The
borates have a reduced risk to non-target organisms.
From the standpoint of reducing environmental
risk, every stick of lumber should be treated with DOT by a dip-diffusion
process before it leaves the lumber mill. This will eliminate the need for
the use of termiticides in home construction and reduce the use of volatile
pesticides inside structures.
CONCLUSION
The environmental
advantages of using diffusable borates for wood protection are many. They
can be summarized as follows:
- Very effective in protecting wood against termites, carpenter ants,
wood-boring beetles, and staining and wood rot fungi;
- Invisible when properly applied, most useful for protecting historic
wood artifacts;
- Not volatile, so do not evaporate or pollute indoor air space;
- Odorless;
- Durable, providing wood protection from insect and fungus attack for
years, eliminating repeated treatments;
- Reduce susceptibility to fire; and
- Have low risk to humans and other non-target organisms.
Jim Renfroe
09-Mar-99 |
|
|
