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<br />'EV/J.uAT1I)~~ ('Ir r:COLOi.:tCAt EFFE.CTS DF SILv'ER IOiJTD~. SEEnING AGENT).I
<br />? I <;,-,~:o' 1
<br />;)c"inlllJ 0\. Klein:':' and RiC'hilrd ,'L
<br />
<br />Accumulatio; oi silver iodide from
<br />weather modification ~ill result 1n nc
<br />overt toxicity effects, but may re$1I1:
<br />in a slight d~lay in biological
<br />pro.cesses.
<br />
<br />11 In Steinhoff, H.~J., ",nd J.D. rves (F.ds). 1976. Ecolo!tical impac.ts of snowpack
<br />Mountains. Colorado. San Juan Ecolo~y Project. fl.nal Report. Colorado State
<br />1/ Present address; Dept. of HicrobioloF!),. CcloraJo State liI1:\v., Ft. ColUns. Co.
<br />
<br />ABSTRACT
<br />
<br />The possible effectS of silver iodide seeding agent
<br />accu~ulation in surface soil& of the San Juan area
<br />were investigated by use of laboratory studies in-
<br />volv:1ng Arthrobaccer - silver interactions. treatment
<br />of soils with varied forms alld level!! of silver, by
<br />examination of silver gradients surrounding seeding
<br />genetator sites. and by use of treatment plots in
<br />spruce, aspen. and subalpine meadow communities
<br />located in the San Juan snoV augmentation area. Lab-
<br />oratory studies have shown that on a short-term basis"
<br />silver iodide or seeding generator burn mixtures at
<br />hi~her than field concentration show only slight
<br />effects on microbial growth or enzyme function. while
<br />free silver ions, even at part-per-billion levels.
<br />can eaus~marked chanses in microbial activities.
<br />TheSe effects were -le*sened in the presence of sailor
<br />complexing.ions. HOwever, under field conditions on
<br />a 3 year basis, Bilve~ iodide appears to have a great-
<br />er potential fer altering pail decomposer ,functions
<br />than silver from".sUver ion. The presence of sUver
<br />from silver iodide - todium iodide complexes, again at
<br />higher than background levels. in the San Juan target
<br />area led to a gradual increase in soil organic matter
<br />content in spruce.and _aspen surface solIs. No such
<br />incr~a8e was obaerved in the 8ubalpine meadow plot.
<br />Silver from silver nitrate tended to concentrate more
<br />in upper plant portions than silver from silver iodide,
<br />although silve~ from silver iodide was more closely
<br />associated with the plant roots. These effects were
<br />only observed 'using silver levels lo-lOOX expected
<br />field accumulation levels. Based on the available
<br />literature and experiments carried out to date, the
<br />accumulation of silver iodide seedin& agent does not
<br />appear to present an ecological threat. although con-
<br />tinual monitoring of test systems should be carried
<br />out to extend the time period over which this conclu-
<br />sion can be tested.
<br />
<br />OBJECTIVES AND HYPOTHESES
<br />
<br />1.
<br />
<br />To monitor soil microbial activities in the San
<br />Juan area, to determine if possible silver accre-
<br />tion is influencing soil microbial processes.
<br />To analYze treatment plot soils to which various
<br />silver addjtons have been made in aspen, spruce,
<br />and grass communities.
<br />To measure microbial responses to silver gradients
<br />present 1n the vicinity of the pagoas Springs gen-
<br />~rator s1te No. 25. and the Emerald Mountain site.
<br />To determine the existence ot possible sub-lethal
<br />effects 01: varlee SlJ.ver J.eve.Ui ana {u{m~ un
<br />microbial processes. including ettects on mlcrOOl-
<br />al viability and capabilit1es to ttanstorm su~
<br />strates requiring enzymatlc adapcatIOn ana enefgy-
<br />p'roduction processes.
<br />To determine if soil microbes are capable of
<br />transforming silver present as silver 10d~de to
<br />additional silver forms. and to determine physio- .
<br />logical mechanisms which may result in silver
<br />transtormac10ns.
<br />To determine if assay procedures Cor vnricd s11ve~
<br />Corms in soil can be developed.
<br />
<br />2.
<br />
<br />),
<br />
<br />4,
<br />
<br />5,
<br />
<br />6,
<br />
<br />These objectives have
<br />hypotheses:
<br />
<br />.'~-'Hypochesis L
<br />
<br />been summarized in a series of
<br />
<br />'"
<br />
<br />: Hypothesis II. Laboratory studies can give an indic,'l-
<br />tlon of the degree of possible dim1n-
<br />uation of microbial activity which
<br />might result froIll silver ac:cumul...tion.
<br />Ill. Soil bacteria can cause a ~hang( in
<br />silver iodide to forms more e~s:\ly
<br />taken up by plants. This mpdification
<br />of silver form may make it necessary
<br />to carry out experiments under field-
<br />related conditions as much as possible.
<br />
<br />-R,,~ly,..s S~c'f,'onj D';';tf'e.j.-:
<br />
<br />i
<br />
<br />i
<br />: Hypothesis
<br />
<br />,UHMARY
<br />
<br />Based on work carried out on the possible ecolof,icilJ.
<br />effects of silver iodide seeding agent accumulation in i
<br />salls of the San Juan area. the following conclusions
<br />CAn be drawn:
<br />
<br />2.
<br />
<br />The accumulation of silver iodide nucleatin~ agent~
<br />presents lJo_.ov~rt-dan&er to humans, pla.nts or .ani-
<br />I mals. based on available literature and work car-
<br />ried out under this studv for a J \-'ear oer1od. --
<br />Silver 10n can cause decreased grovch and enzYme
<br />-induct 10n 1n a soil Archrobacter sDecies aL1=.l.o.
<br />ppb free silver ion. The effect observed is depen-
<br />dent on other anions and cations preserit. Soil
<br />decreases the activity of free silver ions.
<br />Silver from silver iodide or burn mixtures does
<br />not show such ettects on mlcrobla~ grow~n or en-
<br />zymatic activity. Generally 10-IUU ppm ot AgI
<br />torm silver 1s required to observe effects on
<br />growth, VIability. and enzyme induct1on.
<br />Free silver ion trom ~ilver iodide dissociation at
<br />5~6 ppb can cause'observable effects on micro_
<br />organisms. To achieve this silver level
<br />100-200 ppm of silvei as silver iodide a~e re-
<br />quired.
<br />Microorganisms can cause reduction of free silver
<br />ion or silver iodide to metallic silver. Amine-
<br />type materials may be responsible for this reduc-
<br />tion.
<br />Silver iodide added at 1000 ppm shows no immediate
<br />effects on soil respiration processes.
<br />Attempts to establish respiration indices for test
<br />soils across the impact area vere not successful
<br />due to short-term varrability of soil. moisture and
<br />temperature.
<br />Silver accumulation in the vicinity of two seeding
<br />enerator sites did not cause decreases 1n m1cro
<br />bial respiration. Silver tended to accumu ate and
<br />remain 1n the surl:ace Boil zone In Sp~~e ot ex-
<br />tended vater percolation through the zone.
<br />A subalpine meadow test plot installed for ) years
<br />USing silver iod1de and silver n~trate at I, lU,
<br />100 ppm surl:ace soil levels did not show changes
<br />in decomposer functions which could be relate~to
<br />this treatment. - -.
<br />Silver from silver iodide moved to upper plant por-
<br />tions.to a lesser extent than silver from silver
<br />nitrate.
<br />Silver from silver iodide was more closely associ-
<br />ated with plant roots than silver from silver ion.
<br />After 3 years, silver from these tvo differing
<br />original forms have not equilibrated to forms
<br />which will give similar activities.
<br />In spruce and aspen plots, imposition with silver
<br />iodide tends to be related to increased organic
<br />matter retention in the test systems. No such
<br />relationships were observed with equivalent treat-
<br />ments using silver from silver nitrate (silver
<br />ion) .
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<br />1.
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<br />6,
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<br />B,
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<br />\ 13.
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<br />
<br />augmentation
<br />Volv. Publ..
<br />8052), '
<br />
<br />in the San Juan
<br />Fort Collins.
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