Most modern laundry detergent powders and tablets that do not contain phosphate, contain zeolites. Zeolites are ion exchange builders that replace the water hardness ions (calcium and magnesium) with sodium ions. While there are about 40 known naturally occurring zeolite minerals, there are many hundreds of synthetic zeolites (or synthetic clays) commercially available.  It is from these specifically engineered, synthetic types that products are chosen for commercial use.  Natural zeolites are no longer used because they are less efficient, less consistent and more expensive than their synthetic counterparts. 

Zeolites are insoluble additives in detergent powder formula and are currently loosing favour from both an environmental and performance perspective.  They are neither biodegradable nor degradable by any other means and depending on the environment, into which they are put, can either continue to hold calcium, magnesium and heavy metals or release them into the waterways.  Laundry powders of this type can contain 20 - 40% of these insoluble chemical compounds and so there is a fair amount of very fine insoluble powder floating around in the wash thence to our waterways.