Motor oil is toxic from its organic components, but more importantly from the quantities of highly toxic cadmium and vanadium metals that have worn off of engine components. Detergents, bleach, paints, even salad oil can be hazardous if in high enough concentration and in the wrong place. Most of these toxins end up in our streams, ground water, and water supplies and eventually into the oceans. It is estimated that a very high percentage of pregnancies in humans end in the first weeks of development before a women even realizes that she is pregnant. In sea urchins, an egg my never become fertilized because of something having gone wrong with the sperm.
Environmental factors appear to play a large role.
Pollution from a wide variety of sources can interfere with normal sperm function, as can temperature, lighting, oxygen levels, pH, and agitation. The Environmental Protection Agency, in fact, uses sea urchin development as a measure of environmental pollution in a locality. If you are seriously considering doing experimental work with sea urchin sperm you must use a consistent concentration of sperm in your experiments. This is highly experimental and can be a lot of fun. It is best if the students design their own experiments within the available materials.