Overview
Pathways of pesticide movement in the hydrologic cycle (USGS)[a]
Pesticides are in widespread use throughout the U.S. and the rest of the world.
There are many classes of pesticides including insecticides (pyrethrins
and pyrethroids, n-methyl carbamates, organophosphate insecticides,
organochlorines, biologicals and acaricides), herbicides (chlorophenoxy agents,
pentachlorophenol and dinitrophenolic substances, paraquat, diquat and others),
fungicides, incidental pesticides (insect repellents, arsenical pesticides, fumigants,
rodenticides, synergists, disinfectants and adjuvants) and many others.1
While the chemical nature of pesticides has changed dramatically in the past 50
years, the toxicological considerations associated with pesticide exposure have
become much more complex. Even the basic toxicological routes of exposure have been
enhanced. For example, some foods have been genetically modified to possess pesticide-like
properties. Although generally regarded as "safe" for consumption by consumers,
the long-term toxicological impacts of these products are unknown at this time and
remain a point of controversy among healthcare professionals (GMO's are currently
banned in some countries for this reason). The toxicologist must address all such
complexities to properly assess and characterize pesticide exposures.
The widespread use of pesticides and their ubiquitous distribution in the environment
raises toxicological concerns with respect to potential adverse effects on human
health and the environment. Water is one of the primary routes by which pesticides
are transported from an application area to other locations. The U.S. Geological
Survey illustration (above) illustrates some of the potential pathways for transport
of pesticides through hydrologic systems, which supply water for both humans and
natural ecosystems.2
Pesticide poisoning can be difficult to evaluate due to short half-lives, metabolic
factors, circumstances of exposure and a lack of human epidemiological studies.
Each pesticide has specific toxicological properties which must be assessed according
to the available scientific evidence and the peer-reviewed toxicological literature.
The expert toxicologist must apply these resources objectively
to demonstrate or refute causation to reasonable toxicological certainty. Thus, a
toxicological assessment based on multiple lines of evidence can make a significant
difference in providing scientifically credible toxicological opinions.
It is not possible to provide a comprehensive overview of pesticide toxicology in
this brief section; however, the following paragraphs provide a general outline
of the basic classes of pesticides with which TCAS has gained extensive
toxicological experience, performed numerous toxicological exposure assessments,
produced written reports and provided expert testimony over a period of more than
34 years.
Click on any substance to view the corresponding entry.
Click to view other types of hazardous substances.
Fungicides
Show all results for "Fungicides"
Applying fungicide[w]
As the name implies, fungicides are designed to prevent and eliminate fungus infestations.
Fungicides are used extensively in industry, agriculture and by consumers. Fungicides
protect seed grain during storage, shipment and germination, prevent contamination
of mature crops, berries, seedlings, flowers and grasses, suppress mildews, control
slime in paper pulps, protect carpet and fabrics and have many other uses.
Fungicides vary widely with respect to adverse health effects in humans. There are
many types of fungicides including benzenes, strobilurins, thiocarbamates, ethylene
bis, dithiocarbamates, thiophthalimides, triazoles, copper compounds, organomercury
compounds, organotin compounds, cadmium compounds and organic fungicides. Each type
of fungicide causes different acute and chronic symptoms, based on frequency, duration
and magnitude of exposure. Most short-term exposures result in irritant injuries
to skin and mucous membranes and respiratory irritation. Long-term exposure symptoms
can include headache, nausea, vomiting, dizziness, convulsions, loss of consciousness
photophobia, mental disturbances and nervous system impacts.3
Toxicological considerations with respect to fungicides generally depend on the
concentration, dose and duration of exposure to the particular substance contacted,
inhaled or ingested. Historically, fungicide poisoning in the U.S. was far more
common than at the present time. Some poisonings occurred as a result of consuming
seed grain treated with organic mercury or hexachlorobenzene (both of which were
subsequently banned as seed grain treatments). Most fungicides currently in use in the
U.S. have relatively low toxicity in humans as they tend to be inefficiently
absorbed and methods of application are such that exposure circumstances are greatly
reduced from historical norms.
Nevertheless, systemic poisonings do still occur in spite of recent U.S. EPA and
U.S. FDA regulations designed to protect both manufacturers and the general population.
It should be noted, however, that fungicides have many possible uses and they can be
ingested via other substances than food. For example, TCAS was recently retained
to conduct an investigative toxicological risk assessment of a particular fungicide
proposed for use in medical marijuana cultivation. Please contact our
office for additional information.
Herbicides
Show all results for "Herbicides"
A common herbicide[x]
Herbicides are substances which are toxic to plants and are used to control unwanted
vegetation. Although there are a few purely organic herbicidal agents, the vast
majority presently in common use in the U.S. have a synthetic or chemical basis.
U.S. EPA groups herbicides into four classes of substances: (1) chlorophenoxy herbicides,
(2) pentachlorophenol and dinitrophenolic pesticides, (3) paraquat and diquat and
(4) other herbicides. Each group has particular toxicological properties and these
are addressed independently in EPA guidance.4
Chlorophenoxy herbicides contain chlorophenoxy acids, salts and esters. Acute exposure
symptoms can include nausea, abdominal pain, headache, generalized weakness and
dizziness, elevated body temperature, muscular weakness, peripheral neuropathy and
loss of reflexes. Chronic exposure symptoms can include vomiting, diarrhea, confusion
and bizarre or aggressive behavior. Ingestion of large amounts can produce severe
metabolic acidosis. Most reports of fatal outcomes involve renal failure, acidosis,
electrolyte imbalance and multiple organ failure.5
Pentachlorophenol (PCP) is a general biocide presently registered in the U.S. as
a restricted use pesticide for pressure treatment of utility poles. PCP has been
reported to have fetotoxic and embryotoxic properties. Epidemiologic evidence suggests
exposed women may be at risk for miscarriages, reduced birth weight and infant malformations.
Dinitrophenolic herbicides are nitroaromatic compounds which are highly toxic to
humans and animals. Acute symptoms can include profuse sweating, thirst, fever,
headache, confusion, malaise and restlessness. Chronic exposure can lead to respiratory
distress, cyanosis, tissue anoxia, renal failure, liver damage and death.6
Paraquat and diquat are identified chemically as dipyridyls. Acute exposure symptoms
include burning pain in the mouth, throat, chest or upper abdomen; pulmonary edema,
pancreatitis and renal effects. Chronic symptoms of paraquat can include life-threatening
effects on the gastrointestinal tract, kidney, liver, heart and other organs. Pulmonary
edema and early lung damage may occur within a few hours of severe acute exposures.
Delayed toxic effects can include pulmonary fibrosis and circulatory failure. Diquat
can have severe toxic effects on the central nervous system not typical of paraquat
poisoning, including brain stem infarction, seizures and coma.7
Of the many "other herbicides" classified by U.S. EPA, glyphosate is the
most common. Although glyphosate has low acute toxicity
in mammals, glyphosate-related poisoning is occasionally reported. Symptoms include
gastrointestinal issues, mouth and throat pain, nausea, vomiting, diarrhea and abdominal
discomfort. Chronic or intentional oral exposures have resulted in cardiovascular,
respiratory and renal system failure. Severe poisoning can result in tachypnea, dysrhythmias,
hypotension, non-cardiogenic pulmonary edema, hypovolemic shock, oliguria and respiratory
failure.8
TCAS has conducted causative investigations associated with herbicides,
performed toxicological assessments and/or provided expert testimony subsequent
to being retained by defendants, plaintiffs, prosecutors, state attorney generals
and/or public defenders' offices. Please contact our
office for additional information.
Insecticides
Show all results for "Insecticides"
Insecticides[y]
Insecticides are toxic substances which specifically target insects, insect eggs
and larvae. Unlike fungicides and most other pesticides, insecticides are generally intended
for broad distribution in crop fields and large growing areas. Additionally, insecticides
come in many physical forms and often contain more than one active ingredient, each
of which may exhibit different toxic characteristics. As a consequence, different
insecticides pose different risk levels to humans, non-target insects, pets and
the environment.9
Some insecticides are capable of causing profoundly adverse human health impacts
and research in this area is continuous and on-going. For example, in 2015 the International
Agency for Research on Cancer (IARC) classified dichloro-diphenyl-trichloroethane
(DDT) as a probable human carcinogen with scientific evidence linking it to non-Hodgkin
lymphoma (NHL), testicular cancer and liver cancer.10
U.S. EPA groups insecticides into six substance classes with specific chemical and
toxicological properties: (1) pyrethrins and pyrethroids, (2) organophosphates,
(3) n-methyl carbamates, (4) organochlorines, (5) biologicals and (6) other insecticides.11
- Pyrethrins and pyrethroids contain pyrethrum (the oleoresin extract
of dried chrysanthemum flowers). Crude pyrethrum is a dermal and respiratory allergen
easily absorbed by GI tract and pulmonary membranes. Contact dermatitis and allergic
respiratory reactions (rhinitis and asthma) can occur following exposure. Neurotoxicity
has been rarely observed in humans.12
- Organophosphates are efficiently absorbed by inhalation and ingestion
and some are highly toxic. Acute
exposure symptoms include headache, hypersecretion, spasms, nausea, diarrhea, vomiting,
bronchospasm and bradycardia. Chronic exposure symptoms can include seizures and
respiratory failure. Reproductive issues have also been linked specifically to organophosphate
exposure.13
-
N-methyl carbamates can be absorbed by inhalation, ingestion and dermal routes. Acute exposure
symptoms can include muscle weakness, dizziness, sweating, blurred vision,
incoordination, slurred speech, headache, salivation, nausea,
vomiting, abdominal pain and diarrhea. Chronic exposure symptoms can include coma,
seizures, hypotonicity, hypertension and cardio/respiratory depression.
14
-
Organochlorine pesticide use has been sharply curtailed in the
U.S. as a result of multiple cases of acute neurological toxicity. Acute exposure
symptoms can include sensory disturbances, hyperesthesia, paresthesias, headache,
tremor, confusion dizziness, nausea and vomiting. Chronic exposure symptoms can
include seizures, convulsions, respiratory depression and coma.15
-
Biological pesticides include avermectin, azadirachtin, bacillus
thuringiensis, eugenol, nicotine, rotenone, sabadilla and others. Exposure
symptoms are highly variable based on the specific agents involved. Most can cause
GI irritation; higher doses of nicotine and sabadilla may cause adverse central
nervous system and cardiovascular effects.16
-
Other insecticides include such substances as benzyl benzoate,
borates, chlordimeform, chlorobenzilate, cyhexatin, fluorides, fipronil, haloaromatic
compounds, methoprene, neonicotinoids, propargite and others. As with biological
insecticides, exposure symptoms are highly variable based on the specific agents
involved. Although distinct from the other insecticide classes, each insecticide
must be assessed independently as each substance presents a unique set of toxicological
characteristics.17
TCAS has extensive experience assessing insecticide exposures and has regularly
offered toxicological opinions and conducted exposure investigations. A
recent insecticide exposure case in our toxicological case studies summarizes
the events relating to the death of a man with a history of seizure disorder who
was fatally exposed to a particular insecticide in his unventilated basement apartment.
(Dr. Sawyer was retained by plaintiff in this instance). Please
contact our office for additional information.
Poison Baits
Show all results for "Poison Baits"
Poison Baits[z]
Poison baits are a class of pesticides most commonly used to control rodents and
varmints. Although many products have been on the market for decades, new products
are regularly emerging and regulations governing their use are becoming more stringent.
For example, U.S. EPA recently took action18 to remove
12 D-Con™ brand mouse and rat poison products from the consumer market as they
failed to comply with required safety measures to protect children, pets and wildlife
from accidental exposure to rodent baits. The active ingredients (brodifacoum, bromadiolone,
difethialone and difenacoum) are very toxic and persistent and have been found widely
in non-targeted wildlife.19 Baits containing chlorophacinone,
diphacinone, warfarin, cholecalciferol and bromethalin are less toxic, but any rodent
bait has the potential to harm non-targeted wildlife. Recent regulatory changes imposed
on poison bait products containing persistent pesticide ingredients (previously
marketed to residential consumers) are now available only for commercial use by
licensed professionals.
TCAS has significant experience in assessing and solving homicide matters
and assessing the toxic health effects of pesticides and poison baits, as well
as providing written reports and expert testimony in accordance with federal, state
and local regulations. Please
contact our office for additional information.
Notes and References
- U.S. Environmental Protection Agency, "Recognition and Management of Pesticide Poisonings: Sixth Edition," 2013.
- USGS, "Pesticides in Ground Water - Converse County, Wyoming, 2003-04," February, 2014.
- U.S. Environmental Protection Agency, "Recognition and Management of Pesticide Poisonings: Fungicides," 2013.
- U.S. Environmental Protection Agency, "Pesticide Poisoning Handbook, Section III: Herbicides," 2013.
- U.S. Environmental Protection Agency, "Pesticide Poisoning Handbook, Chapter 10, Chlorophenoxys," 2013.
- U.S. Environmental Protection Agency, "Pesticide Poisoning Handbook, Chapter 11, Pentachlorophenol and Dinitrophenolic Pesticides," 2013.
- U.S. Environmental Protection Agency, "Pesticide Poisoning Handbook, Chapter 12, Paraquat and Diquat," 2013.
- U.S. Environmental Protection Agency, "Pesticide Poisoning Handbook, Chapter 13, Other Herbicides," 2013.
- National Pesticide Information Center, "Insecticides," September, 2015
- Voice of America, "WHO Agency Says Insecticides Lindane, DDT Linked to Cancer"
- U.S. Environmental Protection Agency, " Pesticide Poisoning Handbook, Section II, Insecticides," 2013.
- U.S. Environmental Protection Agency, "Pesticide Poisoning Handbook, Chapter 4, Pyrethrins and Pyrethroids," 2013.
- U.S. Environmental Protection Agency, "Pesticide Poisoning Handbook, Chapter 5, Organophosphate Insecticides," 2013.
- U.S. Environmental Protection Agency, "Pesticide Poisoning Handbook, Chapter 6, N-Methyl Carbamate Insecticides," 2013.
- U.S. Environmental Protection Agency, "Pesticide Poisoning Handbook, Chapter 7, Organochlorines," 2013.
- U.S. Environmental Protection Agency, "Pesticide Poisoning Handbook, Chapter 8, Biologicals and Insecticides of Biological Origin," 2013.
- U.S. Environmental Protection Agency, "Pesticide Poisoning Handbook, Chapter 9, Other Insecticides and Acaricides," 2013.
- U.S. EPA, "Rodenticide Products for Consumers," March, 2013
- California Department of Fish and Wildlife, "Rodenticide Baits," Office of Communications, 2013
Images
- USGS, "Pesticides in Ground Water - Converse County, Wyoming, 2003-04," February, 2014.
- U.S. Department of Agriculture, AgResearch Magazine, "Applying Fungicide"
- Texas Commission on Environmental Quality, "Foliar-Applied Herbicides"
- Voice of America, "WHO Agency Says Insecticides Lindane, DDT Linked to Cancer"
- Poison bait U.S. Forest Service, Silvicultural Methods in Relation to Selected Wildlife Species