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E'.~(._LCATln~: (\':." f.CO:"CX:.iCAL SFFECY5 0: ~::;."'t::, !l~::'!!l:. SE:EV!~::-; ACZ~;T]./ ::'ur.:..ili .:.. ~.:~;~~/ ..r1~: .'_' '~.~r(: ;,,-'.:c: Accuoulac. io~ ot" si IVH iodic:le TrOZ'l" ~eather modification ~ill r~sult in ~c overt toxicity effects, but may resul: in a slight delay in biological pro~esses . !f In 5teinhoff, H.'..J., and J.D. rves (Eds). I'Ho. Ecolosieal impacts of .9t:.o\.lpack ~OUr.t.li:1S, Colorado. ~an Juan tcole!!y Preject. Final Report. Colorado Stace 2/ Present address: Dept. o( Microbiology. Colorado State Gntv.. ft. Collins. Co. ABSTRACT The possible effects of silver iodiG~ seeding agent accu~ulation in surface soils of the San Ju~n area ~ere investibated by use of lrt~oratory studies 1n- volvin~ ArthrobJcter - silver interactions, treatment of soils vith varieG forms ana lo!vels of silver, by examination of silver gradients surrounding seeding generator sites, anc by use of treatment plots in spruce, aSpen, and ~ubalpine ~eado~ communities located in the San Juan SOOl.. augnentat ion area. Lab- oratory studies have sho~~ that on a short-term basis,. silver' iodide or seeding generat.or burn l:Iixtures at hiRher than field concentration sho~ only slight effects on microbial &ro~th or enzyme function, ~hile free silver ions, even at part-per-billion levels, can cause marked chanBes in microbial activities. These effects ~ere lessened in the presence of sailor complexing ions. Hovever. ~nder field conditions on a 3 year basis, silver iodide appears to have a great- er potential for altcring soil decomposer functions than silver from silvc" 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 gradu31 lncrease in soil organic matter content in spruce anc aspen surface soils. ~o such incr~ase ~as observed ~n the subalpine meado~ plot. Silver froQ silver nitrate tended to concentrate more in upper plant portions than silver fro~ silver iodide, although silver froQ silver iodide vas more closely associated vith the plant roots. These effects vere only observed using silver levels 10-100X expected field accumulaeion levels. Based on the available licerature and experi:::ents carried out eo daee, the accumulation of silver iodide seeding agent does not ap?ear to present an ecological threat., although con- tinual monieoring of test systems should be carried ouC co extend the cioe period over vhich this conclu- sion can be eested. OBJECTIVES ANn HYPOrriESES 1. To monitor $oil ~icrobial activities in the San Juan area, to deter~ine if possible silver accre- tion is influencing soil microbIal processes. To analyze treatnent plot SOLIs to ~nlch variouS silver addieons have been made in aspen, spruce, and grass co~~unities. To measure microbial responses co silve~ g~adients present in the vicinity of the Pagosa Springs gen- e.aeor site No. 15, and the Emerald Houncaln SHe. To determine the existence ot pOSSIble sub-lethal effectS at lIar:.ed Sliver .leve.l.:, ana lOll,,:' UII microbial processes, Includlng ettects on mlcrOOl a1 viability and capabilitIeS eo transIor~ suo strates requlrlng enzymaclc adaptation ana energy- p.teduction ~rocesses. To deterolne if soil microbes are capable of transfonmioK silver present as silver ~odlde to_ additional sillier forms, and to determIne phYSIO- logical mechanisms ~hich may result in silver e rans rorma t Ions. To determine :f assay procedures for v~r1ed silve~ formS in soil c~n be developed. 2. ). 4. 5. 6. These objectiv~s have been surr~4rized in a series of hypotheses: -'-.'H::::othesis 1. Hypo~hes is iI. Laborater:-- stuc.i"s can sive an irldica- tion of the degree ~f possible cii~in- un~ion of ~icrobial ~ctivity ~hich ~ibht resule fro~ silv~r accu~uln:ion_ : Hypothcsi5 III. Soil b~cteria tan cause a cha~g~ ir. silver iodide to fo~s ~or~ e~sil: taken up by pla~ts_ .n~s ~ocification of silver form ~~y ~dke it ~ecess~ry to carry out experii':'.enes under fielci- relaeed conditions as ~~ch as ~ossib1e. SV:1X.A..RY -At"1Aly~,'s. -S~<::t,'on5 O';";lIe..d.- Based on ~ork carried Out on the possible ecologic~~ effects of silver iodide seeding agene accumulation in soils of ehe San Juan area, the follo~ing conclusions can be dra~TI: , I. 2. The accumulation of silver iodide nucleatin~ agent~ presents DO_ overt-danJ;.er to hu:nans. plantS' or ani- mals, based on available literature anc uork car- rlec OUt w~der this srudv f~r a J Year ~eriod Silver io~ c~n c~us~ dec~eased ~ro~~h and enz~~e inductIon In a soil Arehroba~ter sDecles at 1-10 ppb free silver ion. The effect obse"Ved is d~pen- dent on other anions and cations present. Soil decreases the activity of free silver ions. Silver fro~ silver iodide or burn =ixtures does not sho~ Such etIeCtS on mlc~ODlal gro~tn or en- z~~tic aCtlv~ty. Generally 10-100 ppm of Agl torm SIlver is required eo observe effeces on gro~th, IIlablllty, ana enzyme lnducelOn. tree silver lO~ tro~ silver iodide dissociation at 5-6 ppb can cause' observable effeces on micro- organiscs. To ach!eve this silver level 100-200 pp~ of silver as silver iodide aTe re- quired. Microorganisms can cause reduction of free silver ion or silver iodide to metallic silver. ~ine- type materials oay be responsible for ehis r~duc- tion. Silver iodide added at 1000 p~ shows no immedia~e effects on soil resoiration processes. Attempts to establish respiration indices for test soils across the impact area vere not successful due to short-ee~ variability of soil.moiscure and temperaeure. Silver accumulation in the Vicinity of tva seeding generator sites did not cause decreases In ~lcro- bial respiration. Silver tended co accu~ulace and ~emain In the sur tate 5011 ZOne In spICe at ~x- tended ~ater perCOlatIon throu~h the zone. A subalpine ~eadow test plot installed [~) yea~s using silv~r lodlde and silver nltrate at 1, lU, 100 ppm surface soil levels did not sho~ changes in decomposer functions ~hich could-De related co this treatment. . Silver from silver iodide moved to upper plane por- tions"co a lesser excent chan silver f~om silver nitrate. Silver from silver iodide \.Ias more closely associ- ated \.11th plane roots than silver from silver ion. After 3 years, silver from these e~o differing original forms have not equilibrated to forms which \.Iill give simila= activities. In spruce and aspen ploes. imposition with silver iodide tends to be related eo increased organic maeter retention in the test Systems. So such relationships were observed with equivalent treat- menes using silver from silver nitraee (silver lon) . 1. ). 4. 5. 6. ). 8. 9. 10. 11. 12. \ 13. , .aug:nentatioQ Unlv. Pub!.. 8052). in t.he Sa.n Juan fort Collins. .,. :.B'- A-8d-2