A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like oil) or anthropogenic in origin (i.e. manufactured materials or byproducts from biodegradation). Pollutants result in environmental pollution or become public health concerns when they reach a concentration high enough to have significant negative impacts. A pollutant may cause long- or short-term damage by changing the growth rate of plant or animal species, or by interfering with human amenities, comfort, health, or property values. Some pollutants are biodegradable and therefore will not persist in the environment in the long term. However, the degradation products of some pollutants are themselves polluting such as the products DDE and DDD produced from the degradation of DDT. Pollution has widespread negative impacts on the environment. When analyzed from a planetary boundaries perspective, human society has released novel entities that well exceed safe levels. Different types of pollutants in the environment Pollutants can be categorized in a variety of different ways. For example, it is sometimes useful to distinguish between stock pollutants and fund pollutants. Another way is to group them together according to more specific properties, such as organic, particulate, pharmaceutical, et cetera. The environment has some capacity to absorb many discharges without measurable harm, and this is called “assimilative capacity (or absorptive capacity); a pollutant actually causes pollution when the assimilative capacity is exceeded. Stock pollutants Pollutants, towards which the environment has low absorptive capacity are called stock pollutants. Examples include persistent organic pollutants like PCBs, non-biodegradable plastics and heavy metals. Stock pollutants accumulate in the environment over time. The damage they cause increases as more pollutant is emitted, and persists as the pollutant accumulates. Stock pollutants can create a burden for the future generations, bypassing on the damage that persists well after the benefits received from incurring that damage, have been forgotten. Scientists have officially deemed that the planetary boundaries safe chemical pollutant levels (novel entities) have been surpassed. Fund pollutants In contrast to stock pollutants, for which the environment has low absorptive capacity, fund pollutants are those for which the environment has a moderate absorptive capacity. Fund pollutants do not cause damage to the environment unless the emission rate exceeds the receiving environment's absorptive capacity (e.g. carbon dioxide, which is absorbed by plants and