Levels in humans are generally 100-100,000x lower than levels in the environment. Generally, the levels we are measuring are in the pptr range, but occasionally they are in the ppq range. Specificity is equally as important, as very small changes in structure can dramatically alter a substance's toxicity. We have to be sure that we are measuring what we say we are and not a compound's sister. If you take a chlorine off a dioxin ring, the toxicity changes 15,000-fold.
Expensive equipment is a necessity for the type of work they do.
State public health laboratories are the primary recipients. Over the past 18 years, researchers at EHLS have developed methods for measuring more than 250 toxic substances in people, including dioxins and furans, PCBs, pesticides, VOCs, PAHs, lead, cadmium, mercury, uranium, thorium, and other metals. We have those methods on the shelf. A lot of times it's just assuring people that they have not been exposed. For those that have been exposed, however, we have to be able to measure the dose, and toxicity is dose.