Part II in a series «
by Shona Kelley
Research Scientist
University of British Columbia

In this second article I will dis-
cuss the toxicology of pesticides,
explain how pesticides enter the
body and describe the type of protec-

. tive equipment needed while work-
ing in a tree nursery.

Measuring Toxicity of Pesticides

Toxicity is the harm which a pes-
ticide can cause when an organism
is exposed to it. We want pesticides
to be toxic to pests and we would
prefer that they were not toxic to
other organisms. Unfortunately this
is rarely the case and all pesticides
are poisonous to some degree.
Pesticides are legal poisons and
should be used only when needed,
as recommended on the labels, and
with knowledge and care.

Pesticides may have acute or
chronic effects. Acute effects are
caused by relatively short, high
level exposures. Chronic effects are
caused by long-term exposure to low
levels. Toxicologists have developed
methods of measuring toxicity and
comparing the toxicity of one pesti-
cide to another.

We measure acute effects with
the LD 50 or the dose required to
kill 50% of a population of test ani-
mals. The dose can be given orally
or held against the skin. LC 50 is
the term used when population of
test animals is exposed to the pesti-
cide in air. These values can vary
widely depending upon the animal
species used, the sex, age, etc. So,
as much as possible, the rules for
testing are now set down in detail
by Agriculture Canada. For all pes-
ticides registered in Canada testing
was done by both the company that
is developing the active ingredient
and.by an independent testing lab.

The trick with LD 50’s is to
remember that the smaller the
number the more toxic the pesti-
cide is. This is because it is
expressed as milligrams of pesticide

pe kilogram of body weight (mg/kg
yw). So, the smaller the number the
less it took to kill the animal and,
hence, the more toxic it is. If you
remember from the last article; the
warning symbols used on the labels
are a “Danger” stop sign, a
“Warning” diamond-shaped sign, or
a “Caution” yield sign. The choice of
this shape is based on LD 50 data
front test animals as shown in Table
Long term feeding studies are
used to assess the effects of chronic
exposure. We measure chronic
effects in several ways.
a) Carcinogenesis - does it pro
duce tumours;
b) Teratogenesis - does it pro-
duce birth defects in developing
fetuses but the change is not
passed on to future generations;
c) Mutagenesis - does it cause
changes in the reproductive
cells which are passed onto
future generations. This can
also be assessed with bacteria
or cells in “test tubes” in tests
like the Ames Assay;
Reproductive effects -
changes in fertility (males and
females). This is not the same
as mutagenesis or teratogene-
sis. Examples are abnormal or
absent sperm, failure of eggs to
develop.

d)

How Pesticides Enter the Body

There are 4 ways for pesticides to

enter the body.

1) INGESTION - in people who do
not work professionally with
pesticides this is their major
source of exposure as pesticides
are found as contaminants in
the food, air, water, etc. (a talk
unto itself). In people who work
ich pesticides ingestion occurs

Ny:

a) smoking, drinking or eating

without washing their

e At Raven Lumber in Campbell River Local 1-363 millworkers are outfit-
ted with protective rubber gloves and aprons. Left to right are Lyle
Blomquist, Richard Devison, Dave Brown, and Rob Grant.

Know what pesticides can do
protect yourselves on the jobsi

e Local 1-80 member Linda Wassel with protective spray gear at
MacMillan Bloedel’s tree nursery near Harmac. She is wearing an effec-
tive chemical cartrage respirator with non-porous rubber jacket and

hands first or;

by leaving cigarettes and
food where it can become
contaminated. Professional
applicators can ingest sub-
stantial amounts by using
their mouth to blow out
plugged spray nozzles. How
many of you will admit to
numb-lips during spray sea-
son?

b)

allows increased levels of pesti-
cides into the body. An open
wound is a virtual injection site!
Figure 1 shows the amount of
parathion absorbed through the
skin on different areas of the
body. Fortunately, this pesticide
is not used in forestry but many
other pesticides that are used
can be absorbed across the skin
to some extent.

2) DERMAL EXPOSURE ~- 3) INHALATION - if the particles
means the pesticide enters the or droplets are small enough
body by passing through the they can be breathed into a part
skin. Don’t confuse this with of the lungs where they can be
rashes caused by pesticides absorbed into the blood. High
which I will discuss later. Many pressure sprayers, ULV
pesticide can break down the sprayers or foggers will produce
skin’s natural barriers and droplets small enough to be
some pesticides are especially inhaled.
designed to penetrate the fat-
containing covering that pro- 4) THROUGH THE EYES - eyes
tects some insects and plants. are well suppbed with blood
Any abnormal skin condition and pesticides in the form of

Toxicity Groups for Pesticides
Warning Symbol Oral LDso Dermal LDso

0-50 mg/kg

WW? over 500 mg/kg

Rates are for parathion. Adapted from Maibach et al. Arch Environ Health

23:208-11.

over 50to 500 mg/kg = over 200 to 1000 aa

:
i

*

over 1000 mg/kg

12/LUMBERWORKER/JUNE, 1992