<unk> s are often referred to according to the type of pest they control.<unk> s can also be considered as either biodegradable<unk> s, which will be broken down by microbes and other living beings into harmless compounds, or persistent<unk> s, which may take months or years before they are broken down: it was the persistence of DDT, for example, which led to its accumulation in the food chain and its killing of birds of prey at the top of the food chain. Another way to think about<unk> s is to consider those that are chemical<unk> s are derived from a common source or production method. Insecticides Neonicotinoids are a class of neuro-active insecticides chemically similar to nicotine. Imidacloprid, of the neonicotinoid family, is the most widely used insecticide in the world. In the late 1990s neonicotinoids came under increasing scrutiny over their environmental impact and were linked in a range of studies to adverse ecological effects, including honey-bee colony collapse disorder (CCD) and loss of birds due to a reduction in insect populations. In 2013, the European Union and a few non EU countries restricted the use of certain neonicotinoids. Organophosphate and carbamate insecticides have a similar mode of action. They affect the nervous system of target pests (and non-target organisms) by disrupting acetylcholinesterase activity, the enzyme that regulates acetylcholine, at nerve synapses. This inhibition causes an increase in synaptic acetylcholine and over-stimulation of the parasympathetic nervous system. Many of these insecticides, first developed in the mid 20th century, are very poisonous. Although commonly used in the past, many older chemicals have been removed from the market due to their health and environmental effects (e.g. DDT, chlordane, and toxaphene). However, many organophosphates are not persistent in the environment. Pyrethroid insecticides were developed as a synthetic version of the naturally occurring<unk>  pyrethrin, which is found in chrysanthemums. They have been modified to increase their stability in the environment. Some synthetic pyrethroids are toxic to the nervous system. Herbicides A number of sulfonylureas have been commercialized for weed control, including: amidosulfuron, flazasulfuron, metsulfuron-methyl, rimsulfuron, sulfometuron-methyl, terbacil, nicosulfuron, and triflusulfuron-methyl. These are broad-spectrum herbicides that kill plants weeds or pests by inhibiting the enzyme acetolactate synthase. In the 1960s, more than crop protection chemical was typically applied, while sulfonylureates allow as little as 1% as much material to achieve the same effect. Biopesticides Biopesticides are certain types of<unk> s derived from such natural materials as animals, plants, bacteria, and certain minerals. For example, canola oil and baking soda have<unk> l applications and are considered biopesticides. Biopesticides fall into three major classes: * Microbial<unk> s which consist of bacteria, entomopathogenic fungi or viruses (and sometimes includes the metabolites that bacteria or fungi produce). Entomopathogenic nematodes are also often classed as microbial<unk> s, even though they are multi-cellular. * Biochemical<unk> s or herbal<unk> s are naturally occurring substances that control (or monitor in the case of pheromones) pests and microbial diseases. * Plant-incorporated protectants (PIPs) have genetic material from other species incorporated into their genetic material (i.e. GM crops). Their use is controversial, especially in many European countries. Classified by type of pest<unk> s that are related to the type of pests are: Type Action Algicides Control algae in lakes, canals, swimming pools, water tanks, and other sites Antifouling agents Kill or repel organisms that attach to underwater surfaces, such as boat bottoms Antimicrobials Kill microorganisms (such as bacteria and viruses) Attractants Attract pests (for example, to lure an insect or rodent to a trap). (However, food is not considered a<unk>  when used as an attractant.) Biopesticides Biopesticides are certain types of<unk> s derived from such natural materials as animals, plants, bacteria, and certain minerals Biocides Kill microorganisms Disinfectants and sanitizers Kill or inactivate disease-producing microorganisms on inanimate objects Fungicides Kill fungi (including blights, mildews, molds, and rusts) Fumigants Produce gas or vapor intended to destroy pests in buildings or soil Herbicides Kill weeds and other plants that grow where they are not wanted Insecticides Kill insects and other arthropods Miticides Kill mites that feed on plants and animals Microbial<unk> s Microorganisms that kill, inhibit, or out compete pests, including insects or other microorganisms Molluscicides Kill snails and slugs Nematicides Kill nematodes (microscopic, worm-like organisms that feed on plant roots) Ovicides Kill eggs of insects and mites Pheromones Biochemicals used to disrupt the mating behavior of insects Repellents Repel pests, including insects (such as mosquitoes) and birds Rodenticides Control mice and other rodents Slimicides Kill slime-producing microorganisms such as algae, bacteria, fungi, and slime molds Further types The term<unk>  also includes these substances: *Defoliants: Cause leaves or other foliage to drop from a plant, usually to facilitate harvest. *Desiccants: Promote drying of living tissues, such as unwanted plant tops. *Insect growth regulators: Disrupt the molting, maturity from pupal stage to adult, or other life processes of insects. *Plant growth regulators: Substances (excluding fertilizers or other plant nutrients) that alter the expected growth, flowering, or reproduction rate of plants. *Soil sterilant: a chemical that temporarily or permanently prevents the growth of all plants and animals, depending on the chemical. Soil sterilants must be registered as<unk> s. *Wood preservatives: They are used to make wood resistant to insects, fungus, and other pests. *Gene drives, a complex genetic mechanism which can be embedded into the genetic material of the target species itself. Instead of killing the target individual it can, kill, eliminate the reproduction of, or suppress the reproductive rate of its descendants. This changes the target population in a more pervasive way and has few or no off-target effects.
Pesticide
Pollutant
Prebiotic 
Biological agent
Antiseptic
Cold medicine
Insecticide
Querulant