Page 1179 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

Water Quality and Contaminants Chapter | 80 1111

VetBooks.ir nitrate-containing drinking water was thought to be due to a measurement of the total amount of sodium and chloride
present in water. Salinity also includes anions, such as
an increased dry period due to lower conception rates.
carbonates expressed as oxides, bromide and iodine
We have never encountered a case of acute nitrate or
nitrite toxicoses due to the consumption of drinking expressed as chlorine, and cations such as calcium, mag-
water, unless the water had been hauled to the animals in nesium, bicarbonate, and sulfate but does not include
a fertilizer tank. Such cases have always involved cattle organic matter.
and occur when the availability of drinking water is dis- The US EPA does not include recommendations for
rupted and drinking water must be hauled to the animals TDS, but the NAS provides criteria for classification of
from someplace else. Such circumstances may occur water based upon TDS content established for the US
when water freezes during stretches of very cold weather Geological Society. Criteria for two classification systems
or the water pump fails and cannot be rapidly repaired. are listed in Table 80.9. Note the differences in the classi-
Deaths often occur relatively rapidly; owners often report fication and the use of brine in both, but with different
finding dead victims within a few meters of the contami- criteria for inclusion in that classification. It has been our
nated water tank. Ocular fluid collected from dead vic- experience that those classifications contribute little to the
tims usually contains nitrate in excess of 100 μg nitrate/ assessment of water quality for animals, as we have never
mL and nitrite in excess of 2 μg nitrite/mL. Ocular fluid encountered an instance where those water classifications
collected from dead victims of forage nitrate toxicosis have been used to describe the TDS content.
usually contains less nitrate than ocular fluid from dead Nevertheless, they are included here.
victims of water nitrate toxicosis. If the fertilizer tank More useful information about the use of saline waters
contained ammonium nitrate, then death may be the for livestock is provided under the section titled “A Guide
result of either excessive ammonia or nitrate exposure, to the Use of Saline Waters for Livestock” in the NAS
and the determination of the exact cause of death is publication, starting on p. 48 (NAS Subcommittee on
mostly academic. Under no circumstances do we recom- Nutrient and Toxic Elements in Water, 1974).
mend that a tank that has contained fertilizer be used to
Several factors need to be considered in assessing the suit-
haul drinking water to animals, even if it has been “thor-
ability of saline water for livestock use, including kind, age
oughly washed out.” Theoretically, a fertilizer tank may
and sex of the animals; pregnancy or lactation status; phys-
be cleaned sufficiently to haul drinking water, but not
ical exertion; climatic conditions; diet and its moisture and
practically.
mineral content; production expectations; water salt con-
tent; access to other water sources; and the adaptation to
available water sources. Weight given to those factors is
Total Dissolved Solids
largely a matter of judgment, but TDS is the single most
“Total dissolved solids” is defined in the NAS publication reliable factor that can be determined.
(NAS Subcommittee on Nutrient and Toxic Elements in
The NAS did not recommend the use of highly saline
Water, 1974) as the concentration of all dissolved consti-
water for livestock but acknowledged that circumstances
tuents in water. “Salinity” is often used synonymously
may arise such that saline water may be all that is readily
with “total dissolved solids,” although that assumes that
available. Table 80.10 lists the guidelines for use of saline
all of the dissolved solids are saline. Salinity is more than

TABLE 80.9 Water Classifications Based Upon Total Dissolved Solid Content
DeWiest Classification (1966) Robinove et al., Classification (1958)
Water Classification TDS Content (mg/L) Water Classification TDS Content (mg/L)
Freshwater ,1000
Brackish water 1000 10,000 Slightly saline 1000 3000
Moderately saline 3000 10,000
Salty water 10,000 100,000 Very saline 10,000 35,000
Brine .35,000
Brine .100,000
Source: Data are from US EPA.