My WebLink
|
Help
|
About
|
Sign Out
Home
Browse
Search
ToxicityOfSilver
CWCB
>
Weather Modification
>
DayForward
>
ToxicityOfSilver
Metadata
Thumbnails
Annotations
Entry Properties
Last modified
7/28/2009 2:31:42 PM
Creation date
6/16/2009 9:57:50 AM
Metadata
Fields
Template:
Weather Modification
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
There are no annotations on this page.
Document management portal powered by Laserfiche WebLink 9 © 1998-2015
Laserfiche.
All rights reserved.
/
22
PDF
Print
Pages to print
Enter page numbers and/or page ranges separated by commas. For example, 1,3,5-12.
After downloading, print the document using a PDF reader (e.g. Adobe Reader).
Show annotations
View images
View plain text
April 2009 <br />Williams and Denholm <br />83 <br />Trace levels of dissolved silver in the presence of <br />FeS are rapidly adsorbed (Bell and Kramer 1999) <br />with any silver remaining in solution as silver sul- <br />fide. Silver thiolate complexes are often the <br />dominant dissolved species in waters with high <br />levels of natural organic matter (Adams and <br />Kramer 1998). <br />At low silver concentratlons, when silver is ad- <br />sorbed onto sulfide particies, the locai presence <br />of a high cancentration of an organic mercaptan <br />can lead to an exchange reactlon leading to the <br />fonnation of a silver thiolate. This process wlll <br />move silver into soluflon phase as either a silver <br />thiolate or as a silver-other-metal thiolate at lev- <br />els of the order of <5 nM. This "dissolved silver" <br />is not bfoavailabie however. <br />In their study, Adams and Kramer (1998) showed <br />(using X-Ray Diffractlon) that dissolved silver ion <br />in the presence of amorphous tron suiflde rapidy <br />equilibrated, to give ultra-trace levels (- 5 ng/L) <br />of silver ion. This concentration !s consistent with <br />that calculated from the solubility product con- <br />stant (see earlier). They also calculated that sul- <br />fur containing ligands, especlally thiols, are more <br />important than chloride until the total sulfur spe- <br />cies is less than 10'13 M(-3.2 x 10'9 mg/L). <br />Bielmyer et al. (2002) have argued that silver <br />thiol complexes domfnate all other dissolved sil- <br />ver species when organic molecules contatning <br />sulfur are present and other metal sulfide con- <br />centrations are negliglble. Silver thiol complexes <br />are bioavailable due to increased lipophilicity and <br />have shown chronic effects in Cer3odaphnia <br />dubia at lower concentrations than for silver ion. <br />in a comprehensive (ultra-clean) study of silver <br />concentrations in tailings and stream sediments <br />and rooted vegetation associated with an old <br />mining site in Canada, Kramer et a/. (1999) <br />looked at, inter alla, the associatlon of silver to <br />acid volatile sulflde ("AVS") ratio. They found <br />AVS at the nanomolar concentration in most <br />samplea. <br />TF?e procedure they used detected many colloidal <br />sulfidea, soluble sutfides and part of the polysul- <br />fldes but not the thiola. Concentratlons ranged <br />from <1 nM to 570 nM. Interesbngly, corra- <br />sponding dissofved oxygen levels were between <br />6.8 to 10.2 mg/L with diasofved apanic carbon <br />leveis of 3.2 to 18.7 mg/L. They noted that, ai- <br />though all water samples wers nearly saturated <br />with respect to atmospheric oxygen, over half the <br />samples had measurable AVS ranging from tens <br />to hundreds of nM. <br />They concluded that the silver is strongly bound <br />to the solid phase and is at low nanogram per <br />litre concentratlons in the apparent soluble <br />phase. Their data Indicate that the majority of <br />the operationally defined saluble (<0.45 Nm) sil- <br />ver ion occurs in the colloidal phase. One con- <br />clusion from their study was that as long as the <br />AVS (mole) >Ag' (mole), Ag` shoutd not accumu- <br />late in plant material. <br />Hirsch (1998) looked at the toxicity of silver sul- <br />fide to the juvenile freshwater amphipod (Hya/ella <br />azfeca), an epibenthic organism that burrows into <br />the sediment surtace. Using sediments from a <br />non-cantaminated source, spiked with varying <br />amounts of silver suMide, there was no difference <br />found in survival rates between treatments and <br />controls up to a level of silver of 753.3 mg Ag/kg <br />sediment. The sedlments had average AVS oon- <br />centrations of 5.35 Nmol/gm and total af9anic <br />carbon values of the order of 1.5%. Hirsch noted <br />that the concentration of AVS in the sediment <br />would have favoured the formation of Ag2S had <br />any free silver fon been present. The reladonship <br />between acid volatile sulfldes and metais is im- <br />portant in predicting bioaccumulatlon in benthic <br />macroinvertebrates (Ankiey 1996). <br />Call et a/. (1999) showed that the capaaty of <br />river sediments to bind silver Pffectively occurs at <br />relebVelY low leveis of Total Organlc Carbon <br />("TOC") and acid volatlle suHides. This capability <br />is important in reducing silver bioavailability in <br />pore waters to which benthic organisms would be <br />exposed. <br />Sediments were spiked with silver nitrate unbl <br />silver ion was detected in the pore water. One <br />sediment, with a TOC of 0.8796 and an AVS of <br />< 0.1 NmoUg was spiked at 2.2 g Ag per kilogram <br />before silver aPpeared in the pore water. <br />in contrast, the other sedimsrrt with a TOC of <br />0.22% and AVS < 0.1 Nmol/g shoWed silver in <br />the pore water at a spiking level of only 0.08 g <br />Ag /kg. The authors believed that the differences <br />might in part be explained by the interactfon of <br />severai sediment characterisdcs such as particJe <br />size distributlon and geochemical compositfon. <br />- Scientific Papers -
The URL can be used to link to this page
Your browser does not support the video tag.