In Poweshiek County, Iowa, there are over 45 confined animal feeding operations, and due to their waste management strategies emissions from the manure, including hydrogen sulfide, often become airborne and reach people living in adjacent communities. The legal limit of hydrogen sulfide in Poweshiek County is 30 ppb for one hour up to seven times per year, and this summer a research group from the University of Iowa is monitoring H2S levels at nearby homes to determine whether levels are in fact within those permitted by the law. As a part of my contribution to this project, I am evaluating whether the DIY photographic paper method of H2S sampling originally designed by Claire Horwell et al. can be applied to CAFO emissions, specifically at levels at or below 30 ppb. I will deploy my samplers side-by-side with the conventional passive samplers in order to calibrate them. It is my hope that, if this method is successful, people living near CAFOs will be able to easily collect reliable data to find out whether they are at any risk from H2S exposure.
• Determine if and how well this method can be applied to CAFO emissions, especially at or below 30 ppb • Find a relatively easy method of quantifying data • Create maps of H2S emissions, possibly using MapKnitter • Promote method to communities to crowd-source H2S monitoring
Making and Light-proofing the Samplers
To make the samplers, I followed the procedure described by Horwell et al. and posted on other Wikis. The only alteration I made was that instead of hanging each strip to dry on a clothespin, I left them face-up on a bed of paper towels for >12 hours, due to lack of a private darkroom. I then needed a way to deploy them in the field such that light could not reach them but air could, so I designed an air sampling box that contains a series of baffles that allow air but not light in:
I cut a hole the size of the lid of a film canister into the bottom of a 4"x4"x4" box.
I designed a baffle template that folds into the box and is taped into place (photo is oriented so front face is on the left). It is cut out of black poster stock to minimize light in the box.
Baffle is folded and taped into place with black duct tape. Rope caulk does a good job of filling cracks at the seams.
The back corner can accommodate up to two samplers (best if taped into place).
Light-proofed! Once the box is sealed shut with more black duct tape, only air can get to the samplers.
As for rain-proofing, if I cannot place the boxes in sheltered areas I plan to cover them each with a plastic plate or bowl.
Testing at Low Concentrations of H2S
I am currently doing a trial run to test whether the samplers can, under laboratory conditions, detect H2S levels at or below 30 ppm. I obtained 6 25-gallon emergency water storage bags and placed two treated photo paper strips in each (film canisters wouldn’t fit through the openings). Each bag was then filled with 0, 5, 10, 20, 30, or 50 ppb of H2S, shaking them every day to ensure even gas distribution. After two weeks, I retrieved and fixed the paper to determine if any darkening has occurred. The results seem to indicate that either this technique is not sensitive enough to detect such low levels of H2S, or that this method of testing was problematic (picture below). I'd like to think it was the latter, as the way the H2S was transferred to the bags could not have been perfectly airtight. It is also possible that despite using rubber stoppers and corks, some gas may have escaped out of the bag during shaking or even just while sitting under the hood. Finally, because the samplers were jostling around for two weeks, their coating may have worn off, or they could have rested face-down against the bag, which would have prevented H2S detection.
Water storage bags holding samplers and low concentrations of H2S
Samplers exposed to low concentrations of H2S for two weeks in water storage bags
Small-Scale First Trial: Inside of a Hog Confinement Facility
A nearby hog farmer graciously allowed me to place three samplers in his confinement barn of 1,200 head. After two weeks, I retrieved two of the samplers, as well as one I set up outside my house in a residential area as a control. I found visible changes in the photo paper, but because the discoloration is cumulative over two weeks it does not indicate that the levels of H2S in the barn are any higher than normal. At this point, I can only confirm that this method shows promise with confined animal feeding operations.
Control (left) and test (center and right) samplers after two weeks of exposure.
The researchers at the University of Iowa are recruiting volunteers who live within one mile of a CAFO in Poweshiek County. I will deploy 40 of my samplers side-by-side with those of the University of Iowa (Sigma-Aldrich radiello radial diffusive samplers) at the homes of the recruits. Each box will contain one sampler from Batch A and one from Batch B, and will remain in place for 14 days, after which time I will retrieve and fix the samplers.
Quantification and Analysis
Horwell et al. used spectrofluorimetry to quantify the amount of sulfide collected in each sampler, but this method requires access to a laboratory and is therefore not realistic for civic science. Instead, I am currently working with quantification of color intensity using the free software ImageJ, which would only require scanning of the test strips. Instructions can be found here (scroll down): http://support.dalton.missouri.edu/index.php/wiki/Public:Quantifying_Color_Intensity/
I tested out this method using an (inverted) image from Horwell et al. and was quite pleased with the result.
Horwell, C.J., A.G. Allen, T.A. Mather, and J.E. Patterson. 2004. Evaluation of a novel passive sampling technique for monitoring volcanogenic hydrogen sulfide. J. Environ. Monit. 6: 630-635.
Horwell, C.J., J.E. Patterson, J.A. Gamble, and A.G. Allen. 2005. Monitoring and mapping of hydrogen sulfide emissions across an active geothermal field: Rotorua, New Zealand. Journal of Volcanology and Geothermal Research 139: 259-269.
Iowa Department of Natural Resources. 2004. Animal Feeding Operations Field Study. Appendix C: Iowa Administrative Code 567 Chapter 32. http://www.iowadnr.gov/Portals/idnr/uploads/air/environment/afo/appendix_c.pdf.