Chemical compound
2,6-Dichlorobenzonitrile (DCBN or dichlobenil) is an organic compound with the chemical formula C6H3Cl2CN. It is a white solid that is soluble in organic solvents. It is widely used as an herbicide.[1]
Mechanism of action
It has herbicidal properties killing young seedlings of both monocot and dicot species.[2] DCBN interferes with cellulose synthesis. DCBN adapted cell walls use minimal amounts of cellulose, instead relying on Ca2+-bridge pectates.[3]
Safety
In 1971 in the U.S. State of California, their department of agriculture reported, "Dichlobenil kills the roots of many species, but not all; further, the killing does not extend much beyond the portion actually soaked."[4]
In 1996, the University of California's Statewide Integrated Pest Management Project reported:
Dosages were difficult to control... and as a result soaking or spraying methods are no longer used.
The current application method involves applying metam-sodium products in foam carriers (similar to shaving cream).[5]
The U.S. Food & Drug Administration (FDA, a major operational division of the U.S. Department of Health & Human Services) mentions "dichlobenil" in a report entitled "Herbicidal suppression of bracken and effects on forage production."[6]
The U.S. Department of Energy - Bonneville Power Administration has reported "high potential" for dichlobenil to enter groundwater.[7]
Residue
According to the US Environmental Protection Agency,[8]
On an acute basis, dichlobenil is practically nontoxic to birds, mammals, honey bees; slightly to moderately toxic to aquatic invertebrates and estuarine organisms; and moderately toxic to fish. Dichlobenil is practically nontoxic to birds on a subacute dietary basis, but insufficient data are available to assess chronic avian toxicity. Dichlobenil is toxic to non-target terrestrial and aquatic plants. Dichlobenil may chronically affect fish at levels as low as 0.33 ppm and may chronically affect aquatic invertebrates at levels as low as 0.75 ppm. The dichlobenil degradate, BAM is slightly toxic to mammals and
practically nontoxic to fish and aquatic invertebrates on an acute basis.
Inland Fisheries Ireland has reported, "The dichlobenil residue in water almost completely dissipates in 5 to 6 months."[9]
U.S. FDA reports on pesticide residue.
[10]
Toxicity and environment
Since 1995, the U.S. National Institutes of Health has warned about potential damage to humans during indoor usage (see products listed, below):
Leave all windows open and fans operating... Put all pets outdoors, and take yourself any your family away from treated areas for at least the length of time prescribed on the label.
[11]
In 2006, the University of Hertfordshire reported on "dichlobenil":
It is no longer approved for use within the EU. It has low solubility, is not highly volatile and has potential to leach into groundwater. It is moderately persistent in soils and very persistent in water. It is moderately toxic to mammals, aquatic organisms, honeybees and earthworms.[12]
The report quotes a European Union regulatory effective date of 2009.[12]
The Inland Fisheries Ireland has reported:
The registration of all dichlobenil products (including Casoron G) was revoked in Ireland from 18th March 2009, under Commission Decision 2008/754/EC of 18th September 2008. A period of grace for the disposal, storage, placing on the market and use of existing stocks expired on 18th March 2010.[9]
The London underground found itself in violation by using dichlobenil in September 2011.[13]
As of 2012, the United Nations' International Programme on Chemical Safety (IPCS) has advised that "the substance can be absorbed into the body by inhalation, through the skin and by ingestion... A harmful concentration of airborne particles can be reached quickly when dispersed... The substance may have effects on the skin. This may result in chloracne."[14] Further, it has advised
The substance is toxic to aquatic organisms. This substance does enter the environment under normal use. Great care, however, should be taken to avoid any additional release, for example through inappropriate disposal.[14]
For personal protection during usage, the IPCS advises:
Particulate filter respirator adapted to the airborne concentration of the substance... Sweep spilled substance into covered sealable containers. If appropriate, moisten first to prevent dusting. Carefully collect remainder. Then store and dispose of according to local regulations.[14]
While the ICPS warns strongly, "Do NOT let this chemical enter the environment," it does not note the contradiction that dichlobenil's usage is on the environment.[14]
The U.S. Centers for Disease Control and Prevention (CDC) follows and cites the ICPS.[15]
Consumer products
United States
This partial list of consumer products with "dichlobenil" as an active ingredient:
Synthesis
Dichlobenil is produced from 2,6-dichlorotoluene via the aldoxime.[1]
