ToxicityOfSilver

• Title: An Assessment of the Environmental Toxicity of Silver Iodide
• Prepared By: Bruce D. Williams and John A. Denholm
• Date: 4/1/2009
• Country: Australia
• Weather Modification - Doc Type: Scientific Study

April 2009 Williams and Denholm 87
In contrast, bivalves showed BCFs that corre-
sponded to the daphnid BCF.
6.4 Bioaccumulation bv Fish
Pelagic camivores such as fathead minnows
showed low bioaccumulation potential compared
with their prey. Other studies involving fish have
shown that concentration of inetals was depend-
ent on its contact with sediment or contact with
the sediment by its prey, rather than trophic posi-
tion within the food chain (Ratte 1999).
The toxicity of rainbow trout to dissolved silver
has been the subject of many studies into the
toxicity of silver ion. These studies have gener-
ally used the highly soluble silver nitrate and
have largely focused on laboratory conditions
although some researchers have considered the
effect of water parameters such as hardness and
DOC (Hogstrand and Wood 1998, Erickson et al.
1998, Rodgers et al. 1987).
Where bioavallability in the presence of these
ameliorating factors has been considered, toxicity
was shown to be reduced.
6.5 Bioaccumulation b Terrestrial Animal
Studies into the effects of silver ions on terrestrial
species are limited. Exposure of earthworms to
increasing concentrations of A92S in artificial soii
did not lead to an accumulation of siiver, but
there was evidence of reduced growth. The No
Observed Effect Concentration ("NOEC") was
given as 62 mg Ag/kg (Hirsch 1998).
Silver has also been found in fur seals and sea
lions in the North Pacific Ocean (Saeki et al.
2001). Some 70% of the body burden was found
in the liver with the remaining silver associated
with body hair and other organs. Their data sug-
gested that bioaccumulation increased with age.
Given the extremely low levels of bioavailable
silver expected to arise from the trial, toxic effects
and bioaccumulation for teRestriel species are
considered unlikely.
7. SNOWY PRECIPITATION ENHANCEMENT
RESEARCH PROJECT
The Act requires that the SPERP must only use
silver iodide as the ice nucleating agent. This is
dispensed through a network af 23 ground gen-
erators placed to the west of the main range of
the Snowy Mountains.
When in operational mode, each generator bums
a-2% solution of silver iodide in acetone (w/w),
at a rate of 1.25 litres per hour. Approximately
20g of silver iodide with an average parGcle size
of 0.06Nm is released from each generator for
each hour of operation.
The average mass of silver iodide used each
year (2004 through 2008) is 17.6 kg, dispensed
from 13 separate locations across a target area
af approximately 1000 square kilometres. A
summary of reagent use statistics are shown in
Table 4 below.
A good overview of the SPERP can be found in
Heggli et al. (2005) and Huggins et al. (2008),
although the reader should note that these pa-
pers pre-date the project expansion described in
Section 1 above.
7.1 Preliminarv Investiaations
Given the location and environmental signifi-
cance of the SPERP target area, an extensive
assessment of the ameliorating factors described
in Section 5 above was undertaken prior to the
commencement of cloud seeding experiments.
The factors examined are shown in Table 5.
Samples were collected from a large number of
sites including proposed generator locations, and
likely points of accumulation in the landscape.
Background ievels of tota{ and bioavailable si{ver
were also determined for all of these samples.
Table 4: SPERP Agl Use Statistics3
Year Total mass of Agl dispensed
(kg)
2ppq' 20.1
2005s 23.2
2006 6.8
2007 15.6
2008 20.1
3 These statistics relate to the original target area
of approximately 1000 kmZ
' Twelve generators in operation dunng 2004
S Thirteen generators in operation for the period
2005 through 2008
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