WMOD00071

• Applicant: Western Weather Consultants
• Project Name: Vail Pass
• Date: 11/1/1984
• Weather Modification - Doc Type: Application

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ABSTRACT

the possible effects of silv~r iodide seeding agent
accumulation in surface soils of the San Juan area
were investigated by use of l~~aratory studies in-
volving Arthrabacter - silver interactions, treatment
of soils with varied forms and l~vels of silver, by
examination of silver gradients surrounding seeding
generator sites, and by use of treatment p:o~s in
spruce, aspen, and subalpine meadow commun1tles
located in the San Juan sno~ augmentation area. Lab-
oratory st~dies have shown that on a short-term basis,"
silver iodide or seeding generator burn mixtures at
hiRher than field concentration show only slight
effects on microbial groY!h or enzyme function, while
free silver ions, even at part-per-billion levels,
can cause ~rked changes in microbial activities.
These effects were lessened in the presence of soil or
complexing ions. However, ~nder field conditions on
a 3 year basis, silver iodlde appears to have a great-
er potential for altering soil decomposer functions
than silver from silver ion. The presence of silver
from silver iodide - sodium iodide complexes, again at
higher than backgro~,d levels, in the San Juan target
area led to a gradual increase in soil organic matter
content in 5p~uce and aspen su~face soils. No such
increase was observed in the subalpine meadoy plot.
Silver from silver nitrate tended to concentrate more
in upper plant portions than silver from silver iodide,
although silver from silver iodide was more closely
associated vith the plant roots. These effects were
only observed using silver levels 10-100X expected
field acc~ulation levels. Based on the available
literature and experiments carried out to date, the
accumulation of silver iodide seeding agent does not
~ppear to present an ecological threat, although con-
tinual monitoring of test systems should be carried
out to extend the time period over ~hich this conclu-
sion can be tested.

OBJECTIVES AND HYPOTHESES

1.

To monitor soil microbial activities in the San
Juan area, to determine if possible silver accre-
tion is influencing soil microb1al processes.
To analyze treatment plot soils to WhlCh varlOUS
silver additons have been made tn aspen, spruce,
and grass communities.
To measure microbial responses to silver gradients
present in the vicinity of the Pagosa ~prlngs gen-
erator site No. 25, and the Emerald Mountain SIte.
To determine the existence ot possible sub-lethal
eftects ot varled SILver LeveLS ana IUlllll:> UII
microbial processes, includ~ng ettects on m~crobl-
al viability and capabilities to transtorm SUb
strates requirlng enzymatlc aaaptatlon and enetgy-
p'roduction processes.
To determine if soil microbes are capable of
transforming silver present as silver 10dide to
additional sil~er forms, and to determine physio
"logical mechanisms which may result in silver
trans format 10ns.
To determine if assay procedures for varied silver
forms in soil c~n be developed.

2.

3.

4.

5.

6.

These objectives have
hypotheses:

.....Hypothesis 1.

been surr~rized in a series of

Accumulation of" silver iodide Trcm
~eather modification ~ill result in no
overt toxicity effects, but may resul.
in a slight delay in biological
pro.cesses.

~:LVE~ !GDID~ SEEDI~G

AGE~T1-/

:-:ich,~" r(:

SL.~:C :

Hypothesis II. Laboratory studies can give an indica-
tion of the degree oi possible dimin-
uatien of microbial activity ~hich
might result fro~ silver accu~ulation.
:Hypothesis III. Soil bacteria tan cause a ch~nge ir.
silver iodide to fo~s more c~sily
taken up by plants. This modification
of silver form may ~ake it necessary
to carry out experi~ents under field-
related conditions as m~ch as possible.

-A,,~IY';5 .s~ct;onj C>":'i1l~-!
,
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SU:1X..o\RY

Based on work carried out on the possible ecological
effects of silver iodide seeding agent accumulation in
soils of the San Juan area, the followi~g conclusions
c~n be drawn:

, ,
1. "The accumulation of silver iodide nu"cleatin~ agent:-
presents D~overt.danRer to h~ans; plants or ani-
mals, based on available literature and work car-
rleo Cut under this studv for a 3 vear oeriod.
2. Silver io~ con C3use decreased ~ro~ih and enz'~e
induction in a soil Arthrobacter species at l-lQ
ppb free silver ion. The effect observed is depen-
dent on other anions and cations present. Soil
decreases the activity of free silver ions.
3. Silver from silver iodide or burn mixtures does
not show such ettects on m1croDlal growtn or en-
zymatic actlvlty. Generally 10-10U ppm at Ag!
torm silver is required to observe effects on
growth, v1ablllCY. and enzyme inductlon.
4. tree silver lon tram silver iodide dissociation at
5-6 ppb can ca~se'observable effects"on micro_
organisms. To achieve this silver level
100-200 ppm of silver as silver iodide are re-
quired.
5. Microorganisms can cause reduction of free sil~er
10n or silver iodide to metallic silver. Amine-
type materials may be responsible for this reduc-
tion.
6. Silver iodide added at 1000 ppm shows no immediate
effects on soil respiration processes.
7. Attempts to establish respiration in~ices for test
soils across the impact area were not successful
due to short-term variability of soil. moisture and
temperature.
8. Silver accumulation in the vicinity of tvO seeding
generator sites did not cause decreases in nlcro-
bial respiration. Silver tended to accumulate and
~em3in in the surface solI zone 1n spIte ot ~x-
tended water percolation through the zone.
9. A subalpine meadow test plot install~d for 3 years
using silver iodide and" slIver nitrate at I, lU,
100 ppm surtace 5011 levels did not shov changes
in decomposer functions ~hich could'be related to
this treatment. .
10. Silver from silver iodide moved to upper plant por-
tions"to a lesser extent than silver frOm silver
nitrate.
11. Silver from silver iodide was more closely associ-
ated with plant roots than silver from silver ion.
12. After 3 years, silver from these tvo differing
original forms have not equilibrated to forms
which will give similar activities.
13. In spruce and aspen plots. imposition with silver
iodide tends to be related to increased organic
matter retention in the test systems. No such
relationships ~ere observed with equivalent treat-
ments using silver from silver nitrate (silver
ion).

!' ~ Steinhoff, H'~.I and J.D. rves (Eds). 1976. Ecolo~ical impacts of s~owpack
!1e~ntains, Colorado. San Juan Ec:olC'~y Projec:t, Final Report. Colorado State
II Present address: Dept. of Microbi01o~y. Colorado State Vniv., ~t. Colltns, Co.

augmentation
Univ. Pub!.,
80523. .

in the San Juan
fort Collins.

us