8273

• UCREFRP Catalog Number: 8273
• Author: U.S. Bureau of Reclamation, U.S. Fish and Wildlife Service, U.S. Geological Survey and U.S. Bureau of Indian Affairs.
• Title: Guidelines for Interpretation of the Biological Effects of Selected Constituents in Biota, Water, and Sediment.
• USFW Year: 1998.
• USFW - Doc Type: \
• Copyright Material: NO

National Irrigation Water Quality Program Guidelines

I

I

metabolism depends on whether organisms
are exothermic ("cold blooded") or endo-
thermic ("warm blooded"). Among exo-
therms, such as fish and invertebrates, higher
temperatur~s cause metabolic rates to rise.
Endotherms, such as birds and mammals,
increase their metabolic rate at lower temper-
atures in order to maintain a constant body
temperature. An elevated metabolism
increases the intake of a toxin and distributes
it more rapidly to sensitive organs within the
body.

Water Chemistry

The effect of any toxin may be altered by
variations in water hardness, pH (acidity /
alkalinity), and dissolved oxygen content.
Water hardness, for instance, causes such
great variation in the toxicity of copper and
zinc that the Environmental Protection
Agency, rather than setting fixed values as the
freshwater criteria for these elements, has
instead established formulas that make the
criteria relative to hardness. (See tables at end
of copper and zinc chapters.)

Disease

It seems likely that populations weakened by
disease would be more susceptible to toxins
and vice versa. According to Sprague (1985),
though, the empirical evidence for this
relationship is scanty. At the very least, the
presence of disease in a population can
complicate the task of interpreting which
deaths and other adverse effects are
attributable to toxins and which are due to
the disease.

Nutrition

A species' susceptibility to toxins may be
affected not only by a shortage of food but
also by variations in the quality of the food.
Organisms obliged to deviate from their

CJ

customary diets may lack crucial vitamins,
minerals, or proteins that playa role in
detoxifying harmful compounds.

I

Sampling Biases

I

Interpretation of field data for plants and
animals can be confounded by a sampling bias
that favors "survivors." Most biological
sampling techniques are designed to sample
live biota. In contaminated environments, live
biota represent "survivors" and, hence, these
are likely to be the organisms that either were
less sensitive to the toxin or had less exposure
to it. Bird eggs are probably less affected by
this bias than other media because they are
sampled without regard for the status of the
embryo inside the egg. So long as the egg is
intact, live and dead embryos have equal
probabilities of being sampled.

I

I

I
I

Off-Site Exposure

I

Some organisms travel considerable distances
and may be exposed to toxins at places other
than the site where they are collected. Many
birds, for example, may feed several kilo-
meters away from their nesting sites. Hence,
responses such as teratogenesis among their
offspring may not be attributable to contami-
nation in the immediate vicinity. Although
this complication is obviously most pro-
nounced in the case of birds, many mammals,
fish, and even insects also travel widely.

I

I

I

Confusion About Measurements

I
I
I

Chemical concentrations in plants, animals,
soil, sediment, and water are measured in
various ways, and there is even greater variety
in the ways these measurements are
expressed. Although all contributors to this
volume have endeavored to clarify both the
type of measurement and the units of measure
for every value presented, some may remain
unclear.

I

I

!P

I
I