Dithiocarbamates are a broad class of organosulfur chemical compounds with varied applications across numerous industries, including agriculture, industrial manufacturing, and medicine. These compounds are a modification of carbamates, where both oxygen atoms have been replaced by sulfur atoms.
Understanding Dithiocarbamates
Dithiocarbamates are characterized by a specific functional group, >N−C(=S)−S−, which includes carbon, sulfur, and nitrogen atoms. They are formed by reacting primary or secondary amines with carbon disulfide, often in alkaline conditions. This chemical structure allows them to readily form stable complexes with various metal ions, a property known as chelation. The presence of two sulfur atoms with lone pairs of electrons contributes to their ability to chelate metals, acting as bidentate ligands.
This chelation ability makes them versatile. Some dithiocarbamates contain a metal atom within their molecular structure, such as maneb (manganese), zineb (zinc), or mancozeb (both manganese and zinc), while others like thiram are metal-free.
Everyday Applications
Dithiocarbamates are widely used in agriculture as broad-spectrum fungicides to protect crops from fungal diseases. Examples include mancozeb, maneb, thiram, zineb, and ziram. These compounds are available as sprays, dusts, or wettable powders for application. Beyond fungicides, some dithiocarbamates also function as herbicides, preventing the growth of broadleaf weeds, or as pesticides against nematodes by inhibiting egg hatching.
In industrial settings, dithiocarbamates play a role in the vulcanization of rubber, a process that improves its durability and elasticity. They serve as accelerators in this process, found in products like tires and various consumer goods. A medical application involves disulfiram (Antabuse), an anti-alcoholic drug whose active metabolite is diethyldithiocarbamate. Disulfiram works by interfering with alcohol metabolism in the body.
Biological Interactions and Health Implications
Dithiocarbamates interact with living organisms through their ability to chelate metal ions and react with thiol groups. This enables them to inhibit enzymes that contain metals like copper, iron, or zinc, or those with thiol groups. This enzyme inhibition contributes to their biological effects, including their fungicidal action.
In humans, exposure to dithiocarbamates, which can occur through skin contact, inhalation, or ingestion, may lead to various health effects. These can include functional changes in the nervous and hepatobiliary systems, hormonal and reproductive disorders, as well as immunotoxicity and cytotoxicity. While some dithiocarbamates have been classified by the World Health Organization (WHO) as hazardous, others like ferbam, maneb, thiram, zineb, and ziram are classified by the International Agency for Research on Cancer (IARC) as “not classifiable as to their carcinogenicity to humans”.
Presence in the Environment
Dithiocarbamates enter the environment through agricultural runoff from their use as pesticides. Once released, their environmental degradation in air, water, and soil is generally rapid, largely due to processes like photolysis (breakdown by light) and hydrolysis (breakdown by water). Despite this relatively rapid degradation, dithiocarbamates are among the most frequently detected pesticides in environmental monitoring programs, including those in the European Union.
The degradation of dithiocarbamates can result in the formation of breakdown products. For instance, ethylenebis-dithiocarbamates (EBDCs) can decompose to form ethylene thiourea (ETU) through heating, photolysis, or metabolism. ETU is water-soluble and mobile, allowing it to be absorbed by plant roots, translocated, and further metabolized into ethylene urea (EU) and other derivatives. The presence of these compounds and their metabolites in the environment can impact non-target organisms, with studies evaluating their short and long-term toxicity on aquatic bioindicators like Daphnia magna.