Preparing for Sampling--Mercury Project

OVERVIEW

This activity prepares the class for the field sampling. Or, as one teacher put it: Prior preparation prevents poor performance. (the British Army puts it more colorfully)

GETTING READY

Materials

  • See the extensive list of equipment below

ACTIVITY PROCEDURE

Getting Ready

Read through the activity and assemble the materials. Your class may also have begun the lists and procedures needed during their Experimental Design work. Your class may not take all the types of samples – so be sure to look at the specific materials list and protocols for your class’ sample type(s). Contact the participating scientist, who will coordinate with the lab regarding arrival of the samples.

Doing the Activity

Prepare to sample:

  • Teachers may use this time to talk about safety and field/lab practices. Even though we’re not using chemicals, treat this as a lab time and nobody should be eating, drinking, or chewing gum. Ensure that no students have allergies to latex or other substances being used. Safety goggles aren’t required for this exercise, but scissors and knives should be handled with care, as always.
  • Also, a brief chat about contaminating samples is in order here, as appropriate. Because we measure mercury at such low levels in the environment and in people, it is pretty easy to contaminate samples. For mercury studies, we wear gloves not to protect ourselves from the samples, but to protect the samples from us! For example, if you have pets their hair could have mercury and pet hair is all over us. Also, anything metal could potentially contaminate a mercury sample because mercury itself is a metal. Therefore, we use stainless steel, plastic, or glass for everything. These materials have been tested by many researchers and are usually free of mercury (at least, at the levels we can detect). Finally, we always use powder‐free gloves for mercury sampling. The talcum powder in regular, hospital‐type latex gloves can have trace amounts of mercury. Use Nitrile or powder‐free vinyl gloves (which can be fairly expensive).
  • Decide whether there will be one person taking notes for the entire class, or if students will work in groups. If working in groups, there need to be at least 3 people per group: one to collect, one to manage the sample bags, and one to take notes. If there’s one person taking notes for all, be sure sampling can proceed one sampling pair at a time so the note taker can pay attention to what’s happening.
  • It’s a good idea to do a dry run with students to practice the sampling. Take a sample of soils or insects or whatever you’re sampling, just don’t keep the samples or send them in. Don’t kill any extra animals – please just test the methods and put them back.
  • Decide with the students what your field data sheets should look like and have students create them (ask students‐ should there be a column for fish weight? fish species? sampling location? water depth? etc.)
  • Use the Stream Sampling Data Sheet (one for each site) to record information about your stream site(s).
  • Are you collecting fish to examine environmental risk through food chain concentration of contaminants? The whole body should be analyzed for tissue residue.
  • Are you collecting fish to assess risk to humans from fish consumption? The fish should be filleted and only muscle tissue sent to the laboratory for analysis.
  • Before any sampling starts, determine how many samples you will have and be sure you have enough sample bags.
  • Choose a labeling system that you will be able to understand when the data come back from the lab. Keep labels short since lab technicians need to type them all into the computer! For example, WHITE PERCH‐1, WHITE PERCH‐2, WHITE PERCH‐3; PICKEREL‐1, PICKEREL‐2, PICKEREL‐3, etc. The labeling system does not matter to anyone except the class. The class needs to be able to interpret the labels later.
  • Each sample will have 2 bags – an inner bag where you will place the sample, and an outer bag which has the label and is there to protect that inner bag from contamination during transportation. So this is where it’s important to have someone keeping track of the bags! Keep the inner bag clean and away from any contamination.
  • Build and assemble all of the field gear needed. Have students brainstorm a list of equipment‐ How will we catch, store, transport the fish, the leaves, the soil, the invertebrates?

Assemble materials:

Here is a generalized list of equipment:

  • Zipper seal bags (Ziploc® bags)– Two for each sample you will collect. These can be regular, grocery store type bags, but be sure they’re unused and have not been sitting open for a long time. We recommend buying a new box of bags specifically for the project. Good lab practices tell us that once the bags have been used for sampling, the whole box of bags should ONLY be used for sampling – so don’t take extras home and put food in them! Even though we’re not dealing directly with chemicals, it’s an important safety habit that lab things stay in the lab and never mix with food.
  • Sharpie marker for sample bag labeling
  • Field book and pencil or waterproof pen
  • Sample “Chain of Custody” sheet
  • Mailing envelope, or have arranged sample pickup/delivery to the lab
  • Poland Spring water (new, fresh bottles). One or two liters should be enough for each sample type.
  • Nitrile gloves – one pair for each person who will collect samples, OR if one person will collect all the samples, one pair for each group of samples you will collect.
  • Fishing gear
  • Student‐generated data sheets (or the Stream Sampling Data Sheet)
  • Coin envelopes
  • Knife
  • Measuring board
  • Balance or scale
  • Field guides or keys
  • Forceps
  • Probe
  • Pliers
  • Aluminum foil
  • Large scissors
  • Small scissors
  • Dissecting microscope
  • Scalpel
  • Fillet knives
  • Biopsy punch
  • Antibiotic salve
  • Laboratory pipette bulb
  • Knife sharpener
  • Dissecting trays/nylon cutting boards
  • Poland Spring Water

Here is an example of a more exhaustive list assembled by Nokomis High School students in 2008.

REFLECTION/ASSESSMENT IDEAS

Have students critique each other as they do their dry runs to look for proper collection techniques and labeling procedures. Additionally, you can use the Field Sampling Checklist (the student version is an MSWord document- you can modify it- please send your modifications to Hannah) and the teacher rubric for the Field Sampling Checklist (the teacher version is an MSExcel spreadsheet- again, please send modifications to Hannah.  These checklists can also be used for after the sampling event, and for initial organization of field data in your classroom.

EXTENSION IDEAS

  1. Why are we using Poland Spring water? Have students go to the Poland Spring water quality report to sleuth out the answer. [If hints are needed, direct them to look for Mercury in the list.]
  2. Mercury in Poland Spring water is listed as ND, which means “Not Detected”. This means that it was lower than the detection limit of the lab instruments they were using. The “MRL” number they are listing is that detection limit. Notice that it can be a different number for each chemical. What is the MRL for mercury? So how much mercury is in their water? [Less than 0.0002 mg/L or ppm, units are the same.]
  3. Typical average mercury in organic soil concentration is about 100‐200 ppb. In litter, about 40 ppb. In insects, probably about the same as litter. Do you think the amount of mercury that might be in the Poland Spring water could contaminate our samples? If students need a hint, have them start by converting everything to the same units – the MRL from Poland Spring and the average hair concentrations. [The answer is that the water has less than 0.2 ppb and soil or insects have around 40‐200 ppb, meaning that the water would have 1000 times LESS mercury than our samples, even if it were right at that MRL.]