Lead is one of the most pervasive and persistent environmental toxins. Even at low concentrations, it is a potent neurotoxin that can disrupt brain development, damage the nervous system, and impair learning and behavior. Its effects extend beyond human health. It is highly toxic to aquatic life, accumulates in sediments, and remains in the environment for decades. In laboratory settings, improper disposal of lead-containing solutions can contaminate water systems and soils, making repair costly and challenging.

Despite these hazards, lead compounds have long been used in chemistry teaching laboratories because they demonstrate clear precipitation reactions and gravimetric principles. However, from an environmental science perspective, continued use of lead in an instructional setting raises concerns about unnecessary exposure risks for students, hazardous waste generation, and the sustainability of chemical education practices.

In our analytical chemistry curriculum, one core experiment involves determining the solubility of lead chloride in water. Students prepare a saturated solution of lead chloride, filter out any undissolved solid, and then analyze the solution using a gravimetric method. In the final step, an additional reagent is added to precipitate an insoluble lead compound, which is then dried and weighed. From these measurements, students calculate the solubility product constant (Ksp) for lead chloride. This lab is highly effective in teaching concepts such as solubility equilibria, precipitation reactions, and gravimetric analysis. However, it generates significant amounts of lead waste, which must be collected and disposed through specialized ways. This process is both environmentally and financially costly and it is the opposite of the principles of green chemistry.

This project, funded by the Sustainability Summer Scholar program in the School of Environment & Sustainability, focused on designing a safe and sustainable replacement for the lead chloride that would still allow students to learn the same concepts. Armita began by performing the original experiment herself to understand its workflow, reaction steps, and the specific learning outcomes it supported. Next, she surveyed potential replacement compounds by comparing their solubility product constants (Ksp) to that of lead chloride. She systematically tested several candidates such as iron chloride, magnesium salts, calcium chloride, calcium sulfate, and zinc salts; redesigning the procedure for each to ensure that the desired reactions would occur and measurements remained accurate. After multiple trials, calcium sulfate emerged as the most suitable replacement. It is inexpensive, widely available, and non-toxic with no special disposal requirements. Most importantly, it precipitates cleanly in aqueous solutions under controlled conditions, allowing students to practice the same analytical techniques taught in the lead chloride lab. By substituting calcium sulfate for lead chloride, we can eliminate toxic lead waste from the analytical chemistry curriculum without sacrificing the quality of instruction.