Most vertebrates metabolize and excrete PAHs relatively rapidly. Fish efficiently absorb methyl mercury, but excrete it very slowly. Healthy animals rapidly excrete excess magnesium in the urine and stool. These glands contain an alkaloid poison which the toads excrete when stressed. Hypothetically, they excrete ions in bile salts. Marine teleosts also use gills to excrete electrolytes. This causes the maternal kidneys to excrete bicarbonate to compensate for this change in pH. To maintain hypotonicity they must excrete excess salt ions. They excrete soluble ammonia and phosphorus (orthophosphate). Bioaerosols can transmit microbial pathogens, endotoxins, and allergens and can excrete both endotoxins and exotoxins. Microbial colonies also excrete many different types of waste byproducts. Sponges eventually excrete nutrients in a form that corals can use. Rabbits excrete both hard and soft fecal pellets. Brachiopods have metanephridia, used by many phyla to excrete ammonia and other dissolved wastes. Marine fish also excrete calcium carbonate during osmoregulation.