Symptoms of Exposure and Toxicity
Exposure to toxic heavy metals is generally classified as acute, 14 days or less; intermediate, 15-354 days; and chronic, more than 365 days (ATSDR). Additionally, acute toxicity is usually from sudden or unexpected exposure to a high level of the heavy metal (eg, careless handling, inadequate safety precautions, or accidental spill or release of toxic material often in a laboratory, industrial, or transportation setting). Chronic toxicity results from repeated or continuous exposure, leading to an accumulation of the toxic substance in the body. Chronic exposure may result from contaminated food, air, water, or dust; living near a hazardous waste site; spending time in areas with deteriorating lead paint; maternal transfer in the womb; or from participating in hobbies that use lead paint or solder. Chronic exposure may occur in either the home or workplace. Symptoms of chronic toxicity, often similar to many common conditions, may not be easily recognized. Routes of exposure include inhalation, skin or eye contact, and ingestion (ATSDR MMGs and ToxFAQs; Anon 1993; WHO 1998; CIS 1999; Roberts 1999; Dupler 2001; Ferner 2001).
Exposure to arsenic occurs mostly in the workplace, near hazardous waste sites, or in areas with high natural levels. Symptoms of acute arsenic poisoning are sore throat from breathing, red skin at contact point, or severe abdominal pain, vomiting, and diarrhea, often within 1 hour after ingestion. Other symptoms are anorexia, fever, mucosal irritation, and arrhythmia. Cardiovascular changes are often subtle in the early stages, but can progress to cardiovascular collapse.
Chronic or lower levels of exposure can lead to progressive peripheral and central nervous changes, such as sensory changes, numbness and tingling, and muscle tenderness. A typical symptom is a burning sensation (“needles and pins”) in hands and feet. Neuropathy (inflammation and wasting of the nerves) is usually gradual and occurs over several years. There may also be excessive darkening of the skin (hyperpigmentation) in areas not exposed to sunlight, excessive formation of skin on the palms and soles (hyperkeratosis), or white bands of arsenic deposits across the bed of the fingernails (usually 4-6 weeks after exposure). Birth defects, liver injury, and malignancy are possible. Arsenic has also been used in homicides and suicides.
Acute lead exposure is also more likely to occur in the workplace, particularly in manufacturing processes that include the use of lead (eg, where batteries are manufactured or lead is recycled). Even printing ink, gasoline, and fertilizer contain lead. Symptoms include abdominal pain, convulsions, hypertension, kidney dysfunction, loss of appetite, fatigue, and sleeplessness. Other symptoms are hallucinations, headache, numbness, arthritis, and vertigo.
Chronic exposure to lead may result in birth defects, mental retardation, autism, psychosis, allergies, dyslexia, hyperactivity, weight loss, shaky hands, muscular weakness, and paralysis (beginning in the forearms). Children, who are particularly sensitive to lead (absorbing as much as 50% of the ingested dose), are prone to ingesting it because they chew on painted surfaces and eat products not intended for human consumption (eg, hobby paints, cosmetics, hair colorings with lead-based pigments, and playground dirt). In addition to symptoms found in acute lead exposure, symptoms of chronic lead exposure could include allergies, arthritis, autism, colic, hyperactivity, mood swings, nausea, numbness, lack of concentration, seizures, and weight loss.
Acute mercury exposure may occur in the mining industry and in the manufacturing of fungicides, thermometers, and thermostats. Liquid mercury, because of its beautiful silver color and unique behavior when spilled, is particularly attractive to children. Children are more likely to undergo acute exposure in the home from ingesting mercury either from a broken thermometer or drinking medicine that contains mercury. Because mercury vapors concentrate at floor level, crawling children are subject to a significant hazard when the mercury is sprinkled throughout the house during religious ceremonies or an accidental spill (Zayas 1996). Mercury spills are difficult to clean up, and mercury may remain undetected in carpeting for some time. Symptoms of acute exposure are cough, sore throat, shortness of breath, abdominal pain, nausea, vomiting, diarrhea, headache, weakness, visual disturbances, tachycardia, hypertension, and a metallic taste in the mouth.
Chronic exposure to mercury may result in permanent damage to the central nervous system (Ewan 1996) and kidneys. Mercury can also cross the placenta from mother to fetus (levels in the fetus are often double those in the mother) and accumulate, resulting in mental retardation, brain damage, cerebral palsy, blindness, seizures, and inability to speak.
Dental amalgam is also suspected as being a possible source of mercury toxicity from chronic exposure. Some physicians suggest that amalgam fillings could be part of the explanation for the explosion of learning problems and autism in children since World War II, a time period corresponding with the introduction and widespread use of mercury amalgam (O’Brien 2001). Studies in both animals and humans have confirmed the presence of mercury from amalgam fillings in tissue specimens, blood, amniotic fluid, and urine (Vimy 1990; Willershausen-Zonnchen 1992; Gebel 1996; Omura 1996; Sallsten 1996; Isacsson 1997). However, according to Dr. Robert M. Anderton of the American Dental Association, “There is no sound scientific evidence supporting a link between amalgam fillings and systemic diseases or chronic illness” (Anderton 2001).
The American Dental Association (ADA) does acknowledge that amalgam contains mercury and reacts with others substances. However, the ADA concludes that amalgam continues to be a safe material (ADA 2009). Researchers reported finding “no significant association of Alzheimer’s disease with the number, surface area, or history of having dental amalgam restoration” and “no statistical significant differences in brain mercury levels between subjects with Alzheimer’s disease and control subjects” (Saxe 1999).
The metallic mercury used by dentists to manufacture dental amalgam is shipped as a hazardous material to dental offices. Although the ADA does not advise removing existing amalgam fillings from teeth, it does support ongoing research to develop new materials that will prove to be as safe as dental amalgam (Anderton 2001). Symptoms of chronic exposure in adults and children could include tremors, anxiety, forgetfulness, emotional instability, insomnia, fatigue, weakness, anorexia, cognitive and motor dysfunction, and kidney damage. People who consume fish more than twice weekly show very high serum levels of mercury.
Acute exposure to cadmium generally occurs in the workplace, particularly in the manufacturing of batteries and color pigments used in paint and plastics, as well as in electroplating and galvanizing processes. Symptoms of acute cadmium exposure are nausea, vomiting, abdominal pain, and difficulty breathing.
Chronic exposure to cadmium can result in chronic obstructive lung disease, kidney disease, and fragile bones. Protect children by carefully storing products containing cadmium, especially nickel-cadmium batteries. Symptoms of chronic exposure could include alopecia, anemia, arthritis, learning disorders, migraines, growth impairment, emphysema, osteoporosis, loss of taste and smell, poor appetite, and cardiovascular disease.
Although aluminum is not a heavy metal, environmental exposure is frequent, leading to concerns about accumulative effects and a possible connection with Alzheimer’s disease (Anon 1993). Acute exposure is more likely in the workplace (eg, unintentional breathing of aluminum-laden dust from manufacturing or metal finishing processes).
Chronic exposure may occur in the workplace from accumulated exposure to low levels of airborne aluminum dust and handling aluminum parts during assembly processes over many years. In the home, we are in constant contact with aluminum in foods and water, cookware and soda cans, and other items with high levels of aluminum (eg, antacids, buffered aspirin, treated drinking water, nasal sprays, toothpaste, and antiperspirants) (Anon 1993; ATSDR ToxFAQs for Aluminum). Citric acid (eg, in orange juice) may increase aluminum levels by its leaching activity.
Aluminum-based coagulants are used in the purification of water. However, the beneficial effects of using aluminum to treat water have been balanced against potential health concerns. Water purification facilities follow a number of approaches to minimize the level in “finished” water (WHO 1998). Symptoms of aluminum toxicity include memory loss, learning difficulty, loss of coordination, disorientation, mental confusion, colic, heartburn, flatulence, and headache.