formaldehyde is a naturally occurring substance, of which human beings produce approximately 1.5 oz a day as a normal part of a healthy metabolism. Formaldehyde also occurs naturally in many fruits, such as bananas, apples, and carrots, and does not bioaccumulate in either plants or animals. Formaldehyde works to fixate the tissue of the deceased. This is the characteristic that also makes concentrated formaldehyde hazardous when not handled using appropriate personal protective equipment. The carbon atom in formaldehyde, CH2O, carries a slight positive charge due to the high electronegativity of the oxygen double bonded with the carbon. The electropositive carbon will react with a negatively charged molecule and other electron-rich species. As a result, the carbon in the formaldehyde molecule bonds with electron-rich nitrogen groups called amines found in plant and animal tissue. This leads to formaldehyde cross-linking, bonding proteins with other proteins and DNA, rendering them dysfunctional or no longer useful. This is the reason for usage of formaldehyde as a preservative, as it thus prevents cellular decay and renders the tissue unsuitable for use as a nutrient source for bacteria. Formaldehyde is carcinogenic in humans and animals at excessive levels because the cross-linking can cause DNA to keep cells from halting the replication process. This unwarranted replication of cells can lead to cancer. Unicellular organisms found in the soil and groundwater are also quite sensitive to cross-linking, experiencing damage at a concentration of 0.3 mg to 22 mg per liter. Formaldehyde also affects aquatic invertebrates, with crustaceans being the most sensitive type. The range of concentration damaging them is 0.4 mg to 20 mg per liter. Formaldehyde released from the cremation of embalmed bodies enters the atmosphere and can remain suspended for up to 250 hours. It is readily soluble in water so it will bond with moisture in the atmosphere and rain down onto plants, animals, and water supplies below. As a result, formaldehyde content in precipitation can range from 110 μg to 1380 μg per liter. These concerns notwithstanding formaldehyde, as a ubiquitous chemical produced by living beings, is eminently biodegradable by both sunlight in air and bacteria in soil and water. The growth of the environment movement has caused some people to consider green burials where there are either no aldehyde-based chemicals used in the embalming process, or there is no embalming process at all. Embalming fluid meeting specific criteria for such burials is commercially