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

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April 2009
Williams and Denholm
79
Detection iimits were stated to be between 2 to 5
ng/L. One site, next to an alpine village, showing
between 3 to 10 times background (10 to 30 ng/
L), was believed to reflect emissions from over-
snow vehicles, chair lifts and fossil fuel emis-
sions. The siiver concentratlon in stream runoff
was below the detection limit of 1x10'7 g/L
(SMHEA 1993).
4. TOXICITY OF SIWER ION
The toxicity of the silver ion (Ag+) in water to a
range of aquatic species has been the subject of
a great number of studies reported in the sclen-
tific literature. These studies have been compre-
hensively reviewed by Eisler (1996), Ratte (1999)
and others.
4.1 Acute Silver Toxicitv
Revfewing the toxicity of Ag` to algae, bacteria
and macroinvertebrates, Taylor (cited by Beli and
Kramer, 1999) recorded silver cflncentrations in
the nanomolar (10 Ng/L) range for threshold ef-
fects. More subtle effects were found at concen-
trations of 10 to 100 ng/L.
Eggs of rainbow trout continuously exposed to
silver ions at 0.17 Ng/L had increased embryotox-
icity and hatched prematurely. The fry also had a
reduced growth rate (Davies et a/. 1978).
CICAD 44 notes that aqueous concentrations of
silver in the range 1• to 5 Ng/L killed sensitive spe-
cies of aquatc organisms including representa-
tive species of insects, daphnids, amphipods,
trout, flounder and dace. Wood et al. (1996)
noted that 96-hr LCm values for freshwater fish
generaliy lie in the range 6.5 to 65 Ng/L.
In a detailed study of the mechanism of toxicity of
silver ion (using silver nitrate), Grosell et al.
(2000) found a difference in tolerance to frse sil-
ver ion between European eels and rainbow trout
of 3 to 4 fold. The 96-hr LCw's ranged from 5 to
70 Ng/L. For trout, the sAver fort inhibitsd both
sodlum ion and chbride bn inAux whereas for
eels only the sodium ion inAux was inhibited.
The key target of inhibition in trout and eeis was
found to be branchial Na`, K'-ATPase, an en-
ryme that drives uptake of Na' needed to
counter diffusive loss of Na` to the hypo-osmoac
environment. Thia is simifar to the findings of
Webb and Wood (1998) and Wood ef al. (1999),
who examined physiological responses in rein-
bow trout rather than toxicity. in each case the
source of the silver ion was siiver nftrate.
In the Australian context, acute silver ion toxicity
is enerally considered to be of the order of 1 x
10' g/L, although the Australian and New Zea-
land GuideNnes for Fresh and Marine Water
Quality (ANZECC and AMRCANZ 2004) give
0.005 Ng/L as a Guideline Trigger Value ("GTV").
The Australian Drinking Water Guldelines
(National Heaith and Medical Research Council
2004) cite a guidellne valu• of total dissolved
siiver of 0.1 mg/L.
In the US the EPA has set a guideline of 4.7 Ng
total Ag/L in water with a hardness of 120 mg/L
as the acute toxic limit. There is no chronic
guideline value.
Freshwater flsh and amphibians appear to be the
most sensitive vertebrates to dissolved silver.
The leopard frog, Rana pip/ens, is among the
most sensitlve amphibians with an LCso of 10 Ng/
L silver ion. The mast sensitive flsh species are
even less tolerant with LC60's befinreen 2.5 and
10 Ng/L.
The ClCAD 44 monograph has tabutated the
range of aquatic species that have been used in
toxicity tests with silver lon. The toxic silver con-
centraaon for each species is also given in CI-
CAD 44.
4.2 Chronic Toxicity of Silver lon
The importance of exposure pathways in sub-
lethal toxicity testing of silver on zooplankton has
been examined by Hook and Fisher (2001).
In their paper detailing a study on the physiology
of silver ion toxicity to freshwater rainbow trout,
Wood et al. (1996) note that during chronic expo-
sure to 0.5 Nq/l. Ag' (as silver nitrate) the prind-
pat sub-lethal effect was a small depression of
plaama Na' and CI'.
Diamond et al. (1990) canied out a seriea of
chronic sitver toxicity tests using a range ot rep-
resentative aquatc species including six inverte-
brates and three flsh species. Their results sug-
gested that some of the invertebrates were more
sensitive than the flsh species tested. As a gen-
erai $tatemo,t cney concluded tnac for Weter a
moderate haMness a chronic value could be ob-
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