EHS 602 Exam 2 Study Guide PDF

Growth and Development - Adults have 37 trillion cells in their bodies and are made up of around 200 cell types. - Potency: the number of possible fates that a cell can acquire. - Decreases with age, and decreases with specialization. Therefore, a cell is most potent wh...

Growth and Development - Adults have 37 trillion cells in their bodies and are made up of around 200 cell types. - Potency: the number of possible fates that a cell can acquire. - Decreases with age, and decreases with specialization. Therefore, a cell is most potent when it is a fertilized egg. - A totipotent embryonic stem cell is capable of dividing and developing to form a complete, mature organism. It is capable of forming many different cell types (across the three germ layers: endoderm, mesoderm, and ectoderm). These stem cells then commit to give rise to differentiated cells with specific functions. Totipotent, pluripotent, multipotent. - Cell determination: how does a stem cell know to become a specific type of cell? - Differentiation requires changes in gene expression, protein expansion, structure, and function. - Waddington’s landscape: illustration shows the path of a pluripotent stem cell. It can take many paths, but once it is committed, it is difficult to go down a different path. - Epigenetics: - Epigenetics helps us regulate gene expression. All cells in the body have the same DNA, but not all have the same genes expressed. - Epigenetic mechanisms are affected by these factors and processes: - Development - Environmental chemicals - Drugs/pharmaceuticals - Aging - Diet - DNA methylation: methyl groups can tag DNA and activate or repress genes. Typically represses. - Histone modification: the binding of epigenetic factors to histone tails alters the extent to which DNA is wrapped around histones and the availability of genes in the DNA to be activated. - Histones bounded up locks DNA away from transcription factors, preventing the DNA from being expressed. - There is stage-specific susceptibility to teratogens. - Organogenesis is particularly sensitive. Developmental Toxicology - Teratogenesis: process of abnormal prenatal development. - Teratogen: agent that causes abnormal prenatal development. - Successfully pregnancy outcomes happen at a surprisingly low frequency. Chemical biological, dietary, and genetic factors have all been linked to adverse developmental outcomes. The cause of 50-70% of birth defects are unknown. - James Wilson’s General Principles of Teratology: general principles about how the developing fetus is impacted by toxicants and how reactions to toxicants may differ. - Windows of Susceptibilty.  - Developmental stage at time of exposure influences outcome. - Organogenesis: - Embryonic stage of organ formation. - Time of maximum sensitivity for malformation. - Fetal period: - Sensitive period of functional deficits and some cancers (9-38 weeks of development). - Types of developmental outcomes: - Embryo lethality. - Malformations. - Growth deficits. - Cognitive defects. - Hyperactivity. - Auditory defects. - Reproductive outcomes. - Cancer. - A link exists between maternal health and developmental toxicity. Maternal factors known to influence development are genetics, disease, nutrition, stress, placental toxicity, maternal toxicity. - Examples of developmental toxicants: - Diethylstilbestrol (DES): - Administered to 2-3 million pregnant women in USA from 1943 to 1970s in order to prevent abortion, miscarriage, and premature labor. - Led to a 40x increase in developing vaginal cancer and left DES daughters infertile at higher rates. - Fetal Alcohol Syndrome: - Alcohol is estimated to be the leading cause of cognitive defects in the US. - Syndrome prevalence ranges from 1 to 300-900 births. - Syndrome includes facial anomalies, heart malformations, and more. - Fetal alcohol syndrome mechanism. - Ethanol competitively inhibits retional. Retional metabolizes into retinoic acid, which is critical for cell signaling, growth regulation, and control in development. - Methyl mercury and Minamata: - Inorganic mercury released into Minamata Bay, Japan was methylated by bacteria. - Methyl mercury is more lipophilic than inorganic mercury and biomagnifies. - Pregnant women who ate contaminated fish gave birth to babies with cognitive deficits and skeletal deformities. - Thalidomide: - Given to pregnant women to ease morning sickness.  - Caused many malformations: ocular, congenital heart disease, intestinal, kidney. - Also increase in number of newborns born without limbs or shortened limbs. - No toxicity apparent in adults. - Oxidative stress is associated with sensitivity to thalidomide limb teratogenesis. - Rats were insensitive to thalidomide limb teratogenesis because it had no effect on the nuclear GSH/GSSG ratio in rat embryonic limbs. However, in rats, thalidomide decreases the nuclear GSH/GSSG ratio in rabbit embryonic limbs. Hence, the redox potential is oxidized, creating oxidative stress. - Maternal exposures (obesity, social behaviors, smoking, and chemicals) can all have effects on offspring. - Mechanisms behind abnormal births can be epigenetic. Epigenetics can be modified by the environment, leading to abnormal gene expression. An abnormal epigenetic status on a metabolic gene can lead to maladaptation, which leads to the formation of non-communicable diseases (obesity, diabetes). This can then be passed down to further generations. (i.e. tobacco smoke exposure in utero causes altered epigenetic reprogramming). Carcinogenesis - Diet and tobacco are huge predictors of cancer. - Neoplasia: new or autonomous growth of tissue. - Benign neoplasm: lesion with expansive growth, slow rates of proliferation, no invasion. - Malignant neoplasm/cancer: invasive lesions, capable of spreading to other issues. - Metastases: secondary growths derived from primary malignant neoplasms. These leave the original organ and disperse in other parts of the body. - Tumor: lesion characterized by swelling or increase in size. - Hyperplasia: - Increase in cell number. - Response to stimulus. - Cells are microscopically normal. - Some cells may increase in size (hypertrophy). - Can be normal growth or a pathological response. - Metaplasia: - Abnormal cell differentiation. - Replacement of mature cells of one type with another. - Maintenance of regular tissue organization. - Is reversible. - Dysplasia: - Abnormal differentiation and maturation. - Partial loss of tissue organization. - Slight increase in cell number.  - Cell structure abnormalities. - Potential reversibility. - Initiation: - A stable, mitotically heritable change. - Rapid, irreversible change. - DNA modification. - Usually caused by genotoxic agent. - Need to undergo a cell division to lock in the mutation. - Usually no enough to induce neoplasm. - Promotion: - Clonal expansion of initiated cell population. - Endogenous or exogenous stimulation of growth. - Tumor promoters are usually non-genotoxic. - Drive cellular proliferation or inhibit apoptosis. - Usually requires repeated or constant exposure. - Often organ-specific effects. Different organs have specific growth requirements. - Progression: - Conversion of benign lesion to invasive cancer. - Acquire additional DNA mutations due to rapid rate of cell division (typically large scale, like chromosomal translocations). - Outgrow surrounding cells. - Attract own nutrients via angiogenesis. - Invade surrounding stroma, metastasize to other tissues. - Key genes must be disrupted for cancer to thrive: - Tumor suppressor genes. - Normally protects cells from developing into cancer cells. - DNA repair, apoptosis, cell cycle regulators. - Oncogenes. - A gene that has potential to cause cancer (when mutated) – referred to as a proto-oncogene when not mutated. - Usually cause cells to proliferate when they shouldn’t or ignore apoptosis signals. - Hallmarks of cancer: - Sustaining proliferative signaling. - Evading growth suppressors. - Activating invasion and metastasis. - Enabling replicative immortality (cancer cells can make their telomeres longer). - Inducing angiogenesis. - Resisting cell death. - Avoiding immune destruction. - Unlocking phenotypic plasticity through dedifferentiation that leads cancer cells to regain potency. - Characteristics of cancer stem cells: - Small fraction of tumor.  - Usually dormant. - Can survive for extended periods of time and through many cell divisions. - Overexpress developmental pathway.s - Resistant to drug treatments because of upregulation of drug efflux pumps like ABC transporters or multi-drug resistant proteins. - Now thought to be responsible for invasion and metastasis. - A cancer stem cell (CSC) is a small subpopulation of cells within a tumor that have the ability to self-renew and differentiate into various cell types that make up the tumor. These cells are considered to be the "root" of the cancer, driving its growth and recurrence. CSCs are biologically distinct from the other cells in the tumor, which are more differentiated and less capable of sustaining the tumor on their own. In contrast, the actual tumor consists of a mass of cancerous cells that have proliferated from the original cancer stem cells. While the tumor includes CSCs, it also contains a variety of other cells that contribute to the tumor's structure and function but do not have the same self-renewing and differentiating capabilities as CSCs. - A toxicant is a carcinogen if it does any of the following: - Increase the incidence of tumors. - Decrease the age of tumor development. - Induces rare or unusual tumors. - Increases the multiplicity of tumors. - Three general classes of carcinogenic agents: - Biological agents. - Physical agents. - Chemical agents. - Genotoxic vs. non-genotoxic carcinogens: - Genotoxic: compounds that interact with DNA to modify or change its structure. - Mutagenic. - Can be complete carcinogens (an exposure that by itself is enough to cause cancer). - Tumorigenicity is dose-responsive. - No theoretical threshold effect. - Non-genotoxic: do not directly interact with nuclear DNA, but influence carcinogenesis through alternate mechanisms. - Nonmutagenic. - Threshold effect, potentially reversible. - Tumorigenicity is (usually) dose-responsive. - Can be tumor promoters. - Tissue, species, sex specific. - Genotoxicity and DNA repair: - Direct-acting genotoxic compounds: - Do not require metabolic activation. - Typically carcinogenic in all species at all tissue sites. - Usually are highly reactive electrophilic compounds (wants to bind to negatively charged things such as DNA.  - Ex. mustard gas. - Indirect-acting genotoxic compounds: - Require metabolic activation to form an intermediate that can interact with DNA. - Makes up a majority of DNA interacting compounds. - Usually cause cancer at site of metabolism, not exposure. - Ex. Benzo(a)pyrene. - Mechanism of DNA repair – Double Strand Breaks - Non-homologous end joining: more error prone! Does not repair damaged parts, but rather glues broken pairs together. - Homologous recombination: less error prone! Single stranded DNA looks for a similar DNA sequence to use as a template in repair. - Individual susceptibility to cancer: BRCA. - Cells with BRCA mutations are deficient in homologous recombination repair capacity, leaving NHEJ as the only source of repair. This is error prone which is why cancer is easily able to form and spread! - Non-genotoxic carcinogenesis: - Cytotoxicity: - High dose of chemical induces sustained cell death. - Organ compensates by persistent regenerative growth (rife with DNA mutations). - Mutated cells can accumulate, forming preneoplastic focal lesions and eventually tumors. - Oxidative stress: - Toxicants can induce oxidative stress but also affect cellular antioxidant defense. - Toxicants can create reactive oxygen species that activate molecules or trigger cascades that lead to the transcription of target genes → cell proliferation. - We can try to treat cancer with antioxidants. However, antioxidant supplementation may only help prevent cancer initiation but could actually increase tumor promotion and progression by stimulating cancer stem cell self-renewal. - Inflammation: - Response to continued stimulus (such as chronic toxicant exposure). - Mediated by monocytes and macrophages. - Will release ROS to destroy source of inflammation. - Environmental factors that influence chronic inflammation: - Obesity. - Smoking. - Diet.  - Heavy metals. - Phthalates. - Organochlorine pesticides. - Receptor-mediated: - Toxicants interact with receptors to induce changes in gene expression. - Usually related to proliferation, metabolism, and differentiation. - Ex. Benzo(a)pyrene carcinogenicity is lost in mice lacking the aryl hydrocarbon receptor (AHR). - If a mouse is lacking the HAR receptor, the AHR ligand cannot trigger a cascade, which leads to no transcription factor binding. This leads to no expression of CYPs, which prevents the toxicant from being metabolized and toxified, leading to no DNA damage. - Cancer epigenetics: cancer cells with turn off or methylate some genes such as tumor suppressor genes, but will unmethylate intergenic regions, which are ancient viral sequences that can copy and paste themselves in our DNA, leading to genome instability. - Assaying carcinogenicity and carcinogen classification: - General methods for identification of potential carcinogens: - Short term: - Mutagenesis assays (days to weeks). - Transformation in cell culture (1-3 months). - Medium term: - Qualitative and quantitative analysis of preneoplasia (2-8 months). - Long term: - Chronic bioassays in animals (18-24 months) *gold standard*. - In vitro DNA damage – Comet assay: - Single cell gel electrophoresis. - Damaged DNA is separated from the intact DNA and generates a comet tail. - Measures: - DNA strand breaks. - Oxidative DNA damage. - Cross linking. - DNA repair. - Results produced almost immediately. - In vitro mutagenesis – AMES test: - Prokaryotic mutagenesis test. - Different salmonella strains can test for different types of mutations. - Simulates exposure and toxication/metabolism. - Requires an amino acid. - Long term in vivo testing – two year bioassay:  - Uses rodent models. - Tests 2 to 3 chemical doses from 8 weeks of age, continues throughout lifespan. - Monitors food consumption, bodyweight, clinical observations. - At necropsy, assess tumor number and location, compare to control animals. - Super expensive. - Epidemiological studies of cancer: - Considered strongest evidence of carcinogenicity. - For chemicals – conducted in occupational settings, highly exposed workers. - For dietary components – most data from cohort studies. - Difficulties: - Relies on natural and not experimental exposures. - Individual cancer types are rare. - Most cancers have long latency (time between exposure and onset of symptoms). - Establishing temporality – often have to use a case-control study design with retrospective exposure assessment. - Groups involved in the classification of carcinogens: - International Agency for the Research on Cancer (IARC), part of WHO. - 1 to 4 rating, with 1 showing strong evidence in both humans and animals that the agent is carcinogenic to humans. - U.S. National Toxicology Program. - American Conference of Governmental Industrial Hygienists. - Observe occupational exposures. Neurotoxicology - Nervous system function: - Integrates cell and tissue functions into independent organs (with endocrine system). - Input (sensing) → processing → output (motor). - Central nervous system: brain and spinal cord, protected by skull and vertebral column. - Peripheral nervous system: neurons outside of central nervous system, connect brain and spinal cord to peripheral structures. - Autonomic nervous system: communicates with internal organs and glands. - Sympathetic divison (arousing). - Parasympathetic division (calming). - Somatic nervous system: communicates with sense organs and voluntary muscles. - Sensory. - Motor. - Neuron components: - Dendrites: hairs that receive stimuli. - Cell body/soma: the entirety of the input, protein synthesis. - Axons: transmit stimuli to next cell. - Neural impulse: electrical signal down axon. - Synapse: output, tiny space between signaling and receiving cell. - Not all neurons are myelinated! Only neurons that require faster signaling are myelinated! - Glial (support) cells: - Central nervous system: - Oligodendrocytes: wrap myelin around axons. - Astrocytes: regulate metabolites and ions, blood brain barrier. Provides energy and blocks contaminants from entering CNS. - Microglia: phagocutes, immune cells. - Ependymal cells: line the neural tube cavity, traps and produces cerebral spinal fluid. - Peripheral nervous system: - Schwann cells: wrap myelin around axons. - Satellite cells: surround neuron cell bodies. - Peripheral nerve: bundle of axons. Contains both afferent (sensory) and efferent nerves (motor). - Changing membrane potentials: - Rest: cell membranes polarized (inside is negatively charged, outside is positively charged). - Stimulus: Na+ gates open and Na+ diffuses in the dendrites and soma (depolarization). - Threshold: more Na+ gates open in the axon hillock and Na+ diffuses in the axon (depolarization). - K+ gates open and K+ diffuses out of axon (repolarization). Restores negative charge inside neuron. - Polarization ensures neurons only fire when they should, and depolarization ensures that signals are transmitted rapidly. - Neuron action potentials: - All or nothing event. - One direction down axon. - Neurotransmitter synthesis and release: - Neurotransmitters: chemical messengers. - Made in presynaptic neuron. - Stored in synaptic vesicles. - Glutamate: excitatory neurotransmitter. - GABA: inhibitory neurotransmitter. - Nerve impulse stimulates presynaptic neuron. - Vesicles move to cell membrane and release neurotransmitter. - Neurotransmitter binds receptor:  - Neurotransmitter moves across synaptic cleft and binds to a receptor on a postsynaptic neuron. Receptor may be excitatory or inhibitory. - Neurotransmitter removal after signaling: - Taken back into neuron (reuptake). - Diffuse out of synaptic cleft. - Broken down by enzymes to inactive or into metabolites. - Special protection: blood brain barrier. - Limit access to the brain. - Lipid solubility, size. - Age - Capillary nedotheial cells have tight junctions. - Capillaries syrroudned by astrocyte processes. - Low interstitial fluid protein concentration. - Xenobiotic trasnporters for efflux. - Special risks: - Most neurons postmitotic differentiated statet and thereofre have limited regeneration capability. - High metabolic demand. - High ATP use. - Needs continuous O2 and glucose. - Brain is only 2% of body weight but requires 15% of cardiac output and 20% of O2 consumption. - Consequences: ischemia and hypoxia. - Ischemia: low blood flow. - Prolonged ischemia leads to inappropriate release of glutamate. This causes an increase in intracellular calcium, leading to a calcium cascade. This ultimately leads to brain cell injury and death. - Hypoxia: low oxygen, aerobic metabolism stops. - Less ATP produced, power failure. This leads to Na+/K+ ATPase to not run fast enough, leading to an increase in intracellular Na+. The cell then swells with water and leads to lysis/cell rupture. - Anaerobic metabolism is then used, leading to the production of lactic acid. Low pH damages cell structures. - Sites of neurotoxic injury: - Neuropathy: - Damage to soma (cell body). - Irreversible: injury followed by apoptosis, necrosis. - Risk: high metabolic rate, long cellular process supported by body, excitable membrane. - Cellular conditions: hypoxia, ischemia, hypoglycemia. - Axonopathy: - Axon chemical transection, disconnect in axon. - Regenerated in peripheral nervous system only. - Myelinopathy:  - Myelin loss, swelling, or separation of layers. - Slowing, aberrant conduction. IMpaired ability of neuron to transfer signals. - Neurotransmission interrupted: - Damage to synapse, neurotransmission dysfunction. - Ion channels are various sites across the neuron can experience damage that interrupts transmission as well. - Nervous system timing: - Neural tube defects: - 300,000 annual worldwide. - Can be prevented with folic acid, decreases defects by 19-32%. Air Pollution Toxicology - Bhopal Disaster of 1984. - 40 tons of methyl isocyanate (MIC) were released in the air, drifted 8km downwind to city of Bhopal. - Approximately 580,000 of the 900,000 residents were affected by the gas leak. - MIC is 1.4 times heavier than air. - Survivors often have life-long respiratory and ocular effects. - Clean Air Act of 1970. - Regulation of motor vehicle and industrial source air pollution. - No more acid rain. - Economic success is possible even with regulations. - Indoor air pollution is a major killer in the developing world. - Particle size is not necessarily correlated with health effects. It matters what the PM is made of. - Exercise influences air pollution uptake. - Increased breathing during exercise leads to more inhalation of particles and deeper entry into the pulmonary system. - Experimental methods for air pollution toxicology: - In vitro. - In vivo. - Clinical trials. - Health effects of air pollution: - Many air pollution-related deaths are from rural indoor air pollution from incomplete combustion. - Products of incomplete combustion by far contribute the most to lung cancer. - When one reacts with lung lining, it rips apart polyunsaturated fatty acids, leading to a high immune cell response. This then leads to fibrosis, creating much less space for air to come into the lungs. - Cardiopulmonary effects of air pollution: - Pollution enters olfactory bulb → brain → bad effects.  - Protease (enzymes that break down proteins) action can increase after PM is circulated into the body system (presumably from inflammation) which can damage lung cells. - Cardiovascular effects of air pollution: - Immediate effect: pulmonary oxidatvie stress and inflammation. - Long term effects: - Vasoconstriction. - Hypertension. - Endothelial dysfunction. - CV oxidatvie stress. - Inflammation. - Acute MI. - Chronic atherosclerosis. - Effects of air pollution on the brain: - Leads to inflammation and oxidative stress. - Impacts integrity of BBB. Food Toxicology - The Food, Drug, and Cosmetic Act of 1938 (following the Elixir Sulfanilamide incident). - Presumes that traditionally consumed foods are safe if free from contaminants. - Permits addition of substances to accomplish a specific technical effect is substance is determined to be Generally Regonized as Safe (GRAS) – whole foods are GRAS by default. - A panel of scientific experts base GRAS determination on experimental data but food manufacturers can make “in house” decisions. - Safety labeling essential to protect consumers w ith allergies. - FD&C regulates food coloring additives. - Color of food influences prescription of taste. - Currently, 9 certified synthetic colors are able to used in the US. - Methods for safety evaluation/safety of a substance added to food must be established on: 1. The purpose for the substance. 2. The food to which the substance is added. 3. The concentration level used in proposed foods. 4. The population expected to consume the substance. - Exposure: The Estimated Daily Intake: - Based on: 1. The Daily Intake of the food in which the substance will be used. 2. The Concentration of the food. - Regulators require evidence that the food additive is safe to ensure that the EDI is less than the acceptable daily intake (ADI). - Indirect food additives – substances not directly added to food, but come into contact with food from contacting surfaces – are required by the FDA to be tested to allow foods to be packaged in certain ways. - Safety requirements for dietary supplements: - Supplements are regarded as foods or food constituents and not food additives or drugs. - Safety standard: concept of reasonable expectation of no harm. - Lesser safety standard than reasonable certainty of no harm for food additives. - Rationale: supplement intake is by choice. - Assessment of carcinogenicity: - State of California Safe Drinking Water and Toxic Enforcement Act (Prop 65) – 1986: - State publishes a list of chemicals known to cause cancer ~800 chemicals. - A product must be labeled if it contains a compound expected to lead to >1 extra case of cancer in 100,000 people (over 70 years of consumption). - Manufacturers do not need to disclose what the compounds are, just post the warning. - Adverse reactions to food: allergies. - Immune remediated response – cutaneous reaction and anaphylaxis most common. - Any food can act as an allergen. - Food drug interactions: some foods inhibit enzymes that metabolize the drug, making it more difficult for the drug to be excreted or activated. - Toxicants in food: - Cadmium: - Cd has a half-life of 30 years. - Cd contamination in paddy soil leads to contaminated rice. The Cd targets liver, kidney, and replaces Ca in bone, leading to Itai Itai disease. - Byproducts of cooking: - Heterocyclic amines: form generally from grilling meats, especially when meats are preserved with nitrates. Although super minuscule, it’s still enough to cause DNA adducts which lead to cancer. - Acrylamide: a probable human carcinogen with associations with head and neck, colon, kidney, breast, and ovarian cancer. Formed during high temperature cooking of vegetables, especially potatoes. - PFAS: used as surfactants, estimated half life of 3 years. - Pesticides. - Endocrine disrupting compounds in food contact materials such as BPA and phthalates. - Lead glazed ceramics: high temperatures or highly acidic foods stored in lead-glazed pottery speeds leaching. - Toxins in food: - Aflatoxin: - Indirect genotoxic carcinogen. - Produced by mold.  - One of the most potent cancer causing compounds ever identified. - Similarly to acetaminophen, aflatoxin can be detoxified and excreted. However, when glutathione stores run out, the aflatoxin binds with DNA, creating DNA adducts, leading to cancer. - Most prevalent in areas that are hot and humid that promote mold growth such as Africa and SE Asia. - Toxins in seafood: - Seafood toxins have zero tolerance under FDA policy. - Range of neurotoxins that are acetylcholinesterase inhibitors found in >400 species of fish, oysters, and clams. - Tetrodotoxin (puffer fish) causes CNS paralysis by blocking monovalent cation movement. - Bovine spongiform encephalopathy (mad cow): - Fatal neurodegenerative disease. - Transmitted by prion to humans by eating meat contaminated with brain, spinal cord, or digestive tract of infected animals. Ecotoxicology - Humans have an effect on ecosystems which create a feedback loop. Basically, we are fucking ourselves up. - One health: an interdisciplinary, integrated understanding of animal, human, and environmental health. Everything influences and intersects with each other. Also exposures influence all three disciplines. - One environmental health: understanding the total impact of chemical exposures. - Chemistry drives where pollutants end up: - Speciation of metals can influence bioavailability of dissolved metals (organic vs. inorganic mercury) - Ionization state of chemical. - Lipophilic or hydrophilic. - Bioaccumulation: accumulation of chemicals in an organism from water, air, or soil routes. Occurs when an organism absorbs chemicals fast than it can excrete it. - Bioconcentration: bioaccumulation of a substance from water only. - Biomagnification: increasing concentrations of a chemical in the tissues of organisms at higher levels of a food chain. - Substances which have a high potential for biomagnification are often slowly metabolized or excreted, highly lipid soluble, and slowly broken down in the environment (long half-life). - Toxicity testing: - Typically looks at relevant endpoints (death, reproductive, cancer, developpmental, behavioral) across a range of doses. - Also can have elaborate testing: - Microcosm: representative ecosystems recreated in thet lab that include a number of relevant species.  - Simulated field: create artificial habitats or conduct a study in a habitat enclosure. - Full-scale field study: evaluate the effects of an exposure in a real-life scenario using ecological methods. - Approximately 40% of the global workforce works in agriculture. - US agriculture – susceptibility considerations: - 44% of agriculture employees are self-employed or family members. - Majority of farming establishments have