The NSF grant will support research of soil lead in the US, Chile, UK, and Australia, four regions with distinctive roles in the lead industry. The main goal is to understand how people in each area create knowledge about soil lead, develop and promote methods to reduce exposures, and change the social and economic circumstances in which lead exposures occur. By “following the chemical” across four areas, from lead mines to the soils of urban neighborhoods, there is potential to affect environmental politics and policy, offering new ways to conceptualize the global problem of lead residues, while illuminating possible solutions that are emerging in particular locales.
Colorado State’s Master Gardener program has a guide for estimating soil texture in a variety of ways. One of those ways is a jar method on the last page of the guide. By mixing soil, water, and powdered dish detergent in the jar, then allowing it to sit for two days, and marking the settled level of material at one minute, two hours, and 48 hours, the sand, silt, and clay fractions of the soil can be calculated. Below is an image of the last page describing this jar method.
One of the bulletin boards in the hallway outside of the Ramírez-Andreotta laboratory at the University of Arizona had the following poster that describes how to use red cabbage for measuring pH:
It may be possible to use red cabbage to measure the pH of soils as well. To measure soil pH, soil must first be added to water. To measure soil pH with the red cabbage indicator, soil could simply be added to the indicator solution.
The blog post associated with the poster can be found here. That blog post references an earlier post about using the petals of poinsettia plants in a similar fashion, as they also contain anthocyanin pigments.
Dan left the Ramírez-Andreotta laboratory on January 22 to return to the northeast in preparation for the next stage of the project: collaborative workshops with Troy residents using the Community Soil Study Toolkit in order to identify and address any arsenic, copper, and lead that may be found.
But not before completing the necessary laboratory work to support the Community Soil Study Toolkit and one moonless night in December at the Chiricahua National Monument:
Today Dan visited the Arizona Laboratory for Emerging Contaminants (ALEC) at the University of Arizona where the Troy soil samples prepared in the Ramírez-Andreotta laboratory were sent for analysis using their inductively coupled plasma mass spectrometer (ICP-MS). The director of ALEC, Mary Kay Amistadi, walked Dan through the process of how the Troy soil samples were prepared and analyzed with the ICP-MS to measure the amount of arsenic, copper, and lead in the samples. A small quantity of soil (1 gram) is added to an acidic solution and placed in an industrial microwave to bring all of the metals in the soil into the solution. Then a pump moves the solution into the ICP-MS where it is vaporized and all of the components are measured by their atomic mass.
These laboratory measurements will be used to calibrate the arsenic, copper, and lead field tests of the Community Soil Study Toolkit. By calibrating the tests in the Toolkit, we can use the color responses that they produce to determine the quantities of arsenic, copper, and lead in a soil sample. The preparation of the soils for analysis with the ICP-MS is similar to the preparation in the field tests in the Community Soil Study Toolkit, with a few substitutions: (1) there is no industrial microwave in the field, so the soil is soaked in an acidic solution at room temperature for a longer period of time; and (2) there is no ICP-MS in the field, so a way of generating a color response that corresponds to the amount of arsenic, copper, and lead is substituted.
Below is a picture of the ICP-MS at ALEC:
Today, Dan started a set of experiments to determine the soil texture (percentage of sand, silt, and clay) of the Troy soil samples. Sand, silt, and clay are the main nonliving solid components of soils. The primary difference between sand, silt, and clay particles is their size. The Soil Science Society of America created the graphic below to demonstrate the relative size of sand (largest), silt (middle), and clay (smallest) particles:
Soil texture is a common way to classify soils. It is also relevant for human health if the soil contains lead or other metals. Smaller particles are more likely to stick to our hands when we touch soil, and they are also more likely to be kicked up as dust in the air.
One way to measure soil texture is with a sedimentation experiment. Individual soil particles settle in water at different speeds based on their size. By mixing a soil sample in a column of water and then measuring how it settles over time, the particle sizes in the soil can be calculated. Below is a picture of the sedimentation columns from one set of experiments with the Troy soils:
Another way to measure soil texture is by feel. The USDA created a flow chart so that texture could be determined through a series of steps where soils are rubbed between your fingers. The flow chart can be found here.