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 75
AN ASSESSMENT OF THE ENVIRONMENTAL TOXICITY OF SILVER IODIDE - WITH REFERENCE
TO Ik CLOUD SEEDINCi TRIAL IN THE SNOWY MOUNTAINS OF AUSTRALIA
Bruce D. Wiliiams' and John A. DenholmZ
[1J Former Senior Visiting Research Fellow University of Adelaide, South Australia, Australia
[2] Corresponding author: Snowy Hydro Ltd., Cooma, New South Wales, Australla
AbstracL The objectlves of the Snowy Preclpitation Enhancement Research Project are to determine
the technical, economic and environmerrtal feasibility of augmenbny snowfaNa in the Snowy Mountains
region of New South Wales. The project commenced duting 2004, bllowing proclamation of special ena-
bling legislation, the Snowy Mountains C/oud Seeding Tria/ Act 2004 (NSW). Amongst other things, the
legislatlon prescribed a target area of approximately 1000 square kibmetres (mostly within the Kosa-
uszko Nadonal Park), and scheduled completion date of 2009. The legislatlon also mandated the use of
silver iodide as the seeding agent. The Snowy Mountains C/oud Seed/ng Ti1a! Act 2004 (NSW) was
amended in May 2008, expanding the size of the target area to around 2150 square kilometres, and
authorising the continuation of cloud seeding actlvities untll Aprit 2015. M exfensive revfew of the litere-
ture was undertaken prior to commencement of the project to determine !f the use qf the silver iodide
(Agl) seeding agent would have an adverse impact on the environment. Although silver ions from water-
solubie silver saits have been shown to be toxic to aquatic species, this is not the case for the insoluble
silver iodide. Many studies have shown that the toxicity of silver fon in water is signficantly ameliorated
by the presence in water of chloride fon, carbonate ion, sulfide ion and dissolved organic carbon. In ad-
dition, silver has been shown to strongiy adsorb onto particulate matter in water. Recent research has
shown that silver ion concentrations in natural waters ar+e negligibly small, and an investigation in the
study area has conftrmed many of these amelforating factors to be present. Consequerrtly the bioavail-
ability of silver is unlikely to change from the current background levels. Extensive investigations under-
taken prior to the commencement of the project conftrmed badcground levels of siNer, and the presence
of many ameliorafing factors known to limit toxicity of silver the ion. An analysls of eootoxicity monitoring
data collected over the flrst four years of the SPERP has shown that the monitoring program has suffl-
cfent power to detect any adverse trend in silver concentratlon well before a level of environmentaf con-
cem is reached. The SPERP monitoring results to date have all shown mean concentrations of total sil-
ver to be well below any tevet of concem, and we consider the risk of an adverse ecotoxicologicai impact
resultlng from the use of silver iodide for this project to be negligibly small.
1. INTRODUCTION AND BACKGROUND
The Snowy Precipitation Enhancement Research
Project ("SPERP") is an eleven year doud seed-
ing research program designed to assess the
technical, economic and environmental feasibility
of augmendng snowfalls in the Snowy Mountains
Region of New South Wales ("NSW ).
The SPERP commenced during 2004, foltowing
proclamation of special enabling legislatlon, the
Snowy Mvwrtains Cloud Seedfng Tiie/ Act 2004
(NSW) (the "Act"). Amongst other things, the Act
prescribed a target area of approximately 1000
square kilometres, and a scheduled completlon
date of 2009. The legislation also mandated the
use of silver iodide (Agl) as the seeding agent.
Carespond/rrp author. J.A. Dsnhdm, Snorvy Hydro
Ltd., Cooma, New South Wales, Auatralia. E-msil:
John. [e-mail]
The Ad was amended in May 2008, expanding
the size of the target area to approximately 2150
square kilometres, and providing for a confinua-
dan of cloud seeding activities until Apri12015.
Most of the SPERP target area lies within the
Kosciuszko Nabonal Park ("KNP"), a place with
legislated Australian Natlonal Heritage Signifi-
cance, and also a UNESCO dedared World Bia
aphere Reaervs. A largs propordon of the
SPERP infrastructura and monitoring equipment
is located within the KNP.
Given the environmental setting of the SPERP
target area, a comprehensive invesUgation of the
potentlal environmental impacts was undertaken
prior to commencement of the project in 2004.
This investigation included an extensive review of
the literature:
- Scientific Papers -