The compound 2,6-dichlorophenol is made by female ticks as a sex pheromone. The German cockroach synthesizes two other chlorinated pheromones to induce aggregation (a group of organisms of the same or different species living closely together but less integrated than a society). And chloroform (which was used as an anesthetic during the mid-19th century and is now a common industrial solvent) has a number of natural sources. Termites, emit 15 percent of global atmospheric chloroform, perhaps as a waste product of the chloride compounds naturally present in wood. 

       The tiny poison-arrow frog Epipedo-bates  tricolor is a native of Ecuador that secretes epibatidine, a chlorine containing substance with a unique chemical structure .  The chemical's original purpose is to thwart potential predators.

      Our own species naturally produces the iodinated hormone thyroxine, which regulates basal metabolism and was thought for a hundred years to be the only organohalogen made by the human body. However, recent studies reveal that our bodies produce bleach (hypochlorous acid) and chlorine gas! White blood cells use chloride and the enzyme myeloperoxidase to kill microbial pathogens and perhaps tumor cells. Byproducts of these reactions include chlorinated proteins and nucleic acids. This chlorination process is an essential component of the immune system: Humans deficient in myeloperoxidase are highly susceptible to bacterial infections, particularly pneumonias. Of the few organobromines synthesized by human cells, a bromoester in cerebrospinal fluid, induces REM (rapid-eye-movement) sleep. 

Rocks and volcanoes

     Although living things overwhelmingly utilize organochlorines and organobromines in preference to other halocarbons, fluorine is actually the most abundant halogen in the Earth's crust: Volcanoes emit 11 million tons of hydrogen fluoride and 3 million tons of hydrogen chloride per year. Volcanoes on at least four continents (Asia, Europe, North and South America) emit these naturally formed organochlorine and organofluorine gases. Some of the resulting compounds are identical to some of the  CFCs that catalyze the breakdown of the ozone layer in the stratosphere.

     Rock also contains organohalogens, which can exist as pockets of gas or a component of certain minerals. When some rocks are crushed during mining, methyl chloride, dichloromethane, chloroform, carbon tetrachloride and other chlorinated chemicals are released. Potassium-salt mining releases thousands of tons of chloroform per year. One dark purple fluorite from Bavaria exudes the unmistakable smell of fluorine gas when crushed, earning it the name "stinkspat" among local miners. 

     Halogens aren't confined to terrestrial chemistry: Hydrogen chloride and hydrogen fluoride are also present in space, and at least four meteorites have contained chlorinated compounds.

Significant amounts of nonbiogenic organohalogens come from burning biomass. People set most fires; only 10 percent are caused by lightning or other natural sources. Together, these sources of biomass combustion release large quantities of methyl chloride (900,000 tons per year) and lesser amounts of methyl bromide (10,000 to 50,000 tons per year). The global input per year of atmospheric methyl chloride is estimated at 4 million tons. These figures dwarf the 10,000 tons per year coming from industry.