On May 30th, 2024, a young Virginia opossum appeared in front of the William S. Middleton Memorial Veterans Hospital (VA) in Madison and would not move away when it was approached. Dane County Animal Services Officer Julie Bigley responded to the call, noting that it appeared thin and lethargic, and it had patchy fur. Opossum #24-0983 was admitted to DCHS’s Wildlife Center where Senior Licensed Rehabilitator Kaylie Gilliland assessed its condition. Her notes described several injuries and ailments that were all treatable, if it could receive proper medical treatment, time, and supportive care. However, some issues were more severe than others – the worst of which included having a blood-lead test value of 42.2 𝜇g/dL (micrograms per deciliter). This little lady was suffering from clinical lead toxicosis and had symptoms that matched the condition she was in. 

First, it should be noted that any detectable amount of lead or other heavy metal inside the body of an animal is concerning. An individual that suffers from lead toxicosis may differ in their overall presentation or tolerance level, but no matter the lead value, a number above zero has the potential to cause health complications. Lead toxicosis can cause nutritional problems such as anorexia, weight loss, or diarrhea, and more severely it’s known to induce physiological or neurological changes leading to a loss of vital bodily functions like ataxia, paresis, or organ failure. When blood-lead values are high, from either acute or chronic exposure, an animal may succumb to violent convulsions, coma, or death. Second, even with treatment and rehabilitation, long-term effects from lead toxicity may reduce a patient’s chance of success or release, which has been documented in multiple cases over the years. They might rebound initially and show some signs of progress, but in that time, they are stressed, immunocompromised, and unable to regulate normally. Long-term lead exposure has been attributed to reduced heart and lung functions, which implies lower survivability probabilities for affected wild animals when compared to healthier conspecifics who are more likely to outcompete them for resources. 

According to the Center for Disease Control, a blood lead level greater than 3.5 𝜇g/dL is used as a threshold in human medicine for public health reporting and for starting chelation therapy. Chelation therapy involves administering drugs that are targeted to pull heavy metals out of certain regions of the body, such as blood, bone, or soft tissue. Drugs are given at specific intervals for as long as necessary until the toxin is eliminated. However, success may depend on how an exposure occurred – whether primary or secondary and where the toxin is located. For example, an animal could directly ingest a piece of lead, like a fishing sinker or spent shot from a firearm. That piece of lead would then sit in the stomach to be slowly broken down by strong, gastric acids before moving to other parts of the body. In its base element, lead (Pb +3) can be absorbed in places like bone, organ tissue, or the blood stream, swapping places for other metals like potassium or calcium that have a lower chemical affinity. In human red blood cells, lead has a half-life of 28 to 36 days, meaning that it takes that long for the concentration of the lead to reduce by half. However, lead is also one of the most stable metal elements in existence, so it can last decades in mineralizing tissues like bone or teeth. It can continue to leach into the blood stream if left untreated.  

Imagine a small mammal, like Virginia Opossum #24-0983, snuffling around on the ground and accidentally eating a small, round pellet made of lead. That animal may eventually succumb to mortality from a heavy metal overdose because it didn’t know any better. When it dies, the carcass might become food for something else, like a scavenging Turkey Vulture, American Crow, or Bald Eagle. Or, it could be broken down by other organisms, eventually decaying and leaching into the soils and plants. Bioaccumulation of metals in the environment, or a build-up of particles over time from being in water or food, can become a secondary form of exposure to many animals. Research has suggested that geographic regions with higher soil acidity may break down heavy metals like lead faster, but then they can expose organisms at the base of the trophic food cascade like earthworms. How many native species do you know eat earthworms as part of their regular diet? Using that as an example, the more earthworms that individuals eat means that metal concentrations have a potential to increase bit-by-bit, and eventually the animal could show signs of health decline from chronic, secondary exposure to lead.

At DCHS, blood lead levels greater than or equal to10 𝜇g/dL are treated through chelation, but the records of all tested animals having a value greater than or equal to 3.3 𝜇g/dL are sent to state and federal agencies as part of the rehabilitation reporting process. In the last decade, 762 individuals of 63 different species from all over Wisconsin were admitted to DCHS’s Wildlife Center and had detectable blood-lead levels. In fact, DCHS Senior Wildlife Veterinary Technician Erin Lemley (CVT), along with authors from the Department of Surgical Sciences at the UW-Madison School of Veterinary Medicine, used data from our wild patients to collaborate on a recent publication about evaluating and treating lead toxicosis in avian species. It can be found in the Journal of the American Veterinary Medical Association as of January 10th, 2025 here: https://doi.org/10.2460/javma.24.09.0592  

Sharing this information, while not required for our permitting, gives staff a way to contribute to the growing body of knowledge about lead toxicity and offers us a feeling of purpose in our jobs. Documenting the presence or absence of lead in wild animals is just one of many ways that DCHS’s Wildlife Center provides research that can be used towards educating our community about environmental issues related to public health. Our team also gives voices to the voiceless, illustrating the damaging effects of lead toxicity and how we can prevent it. Removing the source of lead exposure is key – whether that means switching to alternative, non-toxic metals in fishing or hunting practices or advocating for greater clean-up efforts at the local, national, or international levels. 

Lead toxicosis is difficult and expensive to treat, and it may be near impossible to perform in the future due to drug shortages, pharmaceutical price gauging, and manufacturing limitations. For now, we can work with the medications that are available to us and in stock, but how long that will last is unknown. All being said, Virginia Opossum #24-0983 is one of the lucky few who was admitted at the right time and could be treated with oral chelation drugs, which of course she ate right away and whenever any other kind of food was placed in cage. She was released back to her home area after two months of chelation, successfully recovering in rehabilitation. 

Jackie Sandberg is the Wildlife Program Manager at DCHS's Wildlife Center.