Phosphate in Water

Introduction

The amount of phosphate in a water sample will be found by using the TesTab^® color comparison method.

Concepts

• Concentration of phosphate
• Parts per million
• Water testing

Background

Phosphorus is a vital element of life and is usually found naturally in water as phosphate ions. Phosphate originates from fertilizers, wastewater of domestic origin such as human, animal and plant residue and from wastewater of industrial origin. Phosphates are also added to farm and city water systems to control water hardness. Phosphates from laundry detergents can result in overgrowth of algae (also known as algae blooms), which in turn will cause the algae to die at a high rate and undergo decomposition. This decomposition process depletes oxygen from the water and results in increased fish kill. Lakes that have high phosphate levels undergo a process called eutrophication. There are two types of eutrophication: cultural eutrophication and natural eutrophication. Cultural eutrophication is water pollution caused by the excessive amounts of phosphates introduced by human activities. The rapid growth and die-off of plants causes lakes to “fill-in” and age more rapidly (see Figure 1). In contrast, natural eutrophication, which is the process where lakes age gradually and become more productive, requires thousands of years to come to completion. Phosphate levels greater than 0.1 parts per million may lead to an overgrowth of aquatic plants.

Materials

Safety Precautions

Phosphate TesTabs^® contain chemicals that may irritate skin or be harmful if swallowed. The TesTab reagents used in this kit were designed with safety in mind. The single-use, foil-packaged TesTabs are easy to dispense. Store TesTabs in a cool, dry place and only open when ready to use the tablet. A single tablet, either alone or reacted with a sample, is a very low health hazard; however, TesTabs should not be ingested. Wear chemical splash goggles and chemical-resistant gloves. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. In the field, reacted samples may be poured into a container for later treatment. Reacted samples may be flushed down the drain with an excess water according to Flinn Suggested Disposal Method #26b.

Procedure

1. Fill the water sample tube to the 5-mL line with a water sample.
2. Add one Phosphorus TesTab to the tube.
3. Cap the tube and mix until the tablet has dissolved.
4. Wait for five minutes.
5. Compare the color of the sample to the Phosphate color comparison chart.
6. Dispose of the reacted sample according to the instructor and rinse the water sample tube twice with the water sample for the next test.

Teacher Tips

• Enough materials are provided for 15 tests.
• It’s a good idea to collect several water samples from each site that is tested. It is also wise to test the samples within one hour of collection if possible.
• Phosphate TesTabs contain ammonium molybdate which reacts with phosphorus to form a phosphomolybdate complex. This complex is reduced to a blue complex by ascorbic acid.
• A wait of five minutes is required for the overall reaction to take place.
• The range of the phosphate TesTab test is between 0 to 4 ppm.
• TesTabs are a vendor product of the LaMotte Company. SDSs are available through the manufacturer website.