); [EMAIL_ADDRESS] (J.T.I.T)  
3 Pediatric Research Institute, Department of Pediatric, University of Southern Maine, Portland, ME 04101, USA; [EMAIL_ADDRESS] (Correspondence: [EMAIL_ADDRESS])  
S.S.  
have been largely omitted from environmental toxicology studies due to their proximity to death, as it typically takes multiple decades of exposure to result in diseases. Now, our geriatric populations are predicted to live for several decades, and we have limited knowledge of how long-term chemical exposures affect geriatric populations distinctly from younger populations. Environmental pollution interacts with the aging crisis in two critical ways: (1) geriatric populations are often more vulnerable to chemical health threats, and (2) environmental pollutants may act as gerontogens--a class of chemicals that induce or accelerate aging processes [5; 6]. Evidence suggests geriatric individuals are often more vulnerable to the negative health effects of environmental pollution, but age as a biological variable is not a major consideration in toxicology [5]. Many chemicals act as gerontogens, and this number is increasing as more pollutants are considered [6; 7; 8; 9; 10]. To address the interactions between aging and toxicology, we employed a \"Toxic Aging Coin\" approach [10]. On the _heads_ side, we consider how age impacts toxicity, while on the _tails_ side, we consider how chemicals act as gerontogens. Metals are particularly hazardous environmental pollutants, as they are naturally occurring, often in industrial waste and effluent. Many are toxic, and remediation is difficult, as most cannot be metabolized or degraded to less toxic forms. Metals are considered a class of gerontogens, as exposures are linked to all the top 10 most prevalent age-related diseases, and many metals induce hallmarks of aging across multiple tissues (e.g., cellular senescence, telomere attrition, mitochondrial dysfunction) [6; 11; 12; 13; 14; 15; 16]. Chromium is a naturally occurring mental found in the environment in two valence states--trivalent (Cr[III]) and hexavalent (Cr[VI]). Cr(III) is relatively innocuous to human health, while Cr(VI) is regarded as highly toxic and a known human carcinogen [17; 18]. Many reports have shown that Cr(VI) levels in drinking water exceed the maximum contaminant levels set by the World Health Organization (WHO) and the U.S. Environmental Protection Agency (US EPA) at 0.05 and 0.1 mg/L, respectively. Such water contamination is often due to industrial pollution and sometimes due to geogenic sources from ultramafic volcanic bedrock [19; 20; 21; 22; 23]. Cr(VI) exposure may be a risk factor for at least 3 of the top 10 age-related diseases: chronic obstructive pulmonary disease, Alzheimer's disease, and chronic kidney disease [24; 25; 26]. Further, evidence from welders occupationally exposed to Cr(VI) in welding fumes and cell culture studies suggests Cr(VI) acts as a gerontogen [27; 28; 29; 30; 31]. Decades of research have reported Cr(VI) neurotoxicity in cell cultures, animal models (rodents, fish, birds, _Drosophila_), and human populations, but many key knowledge gaps remain [10]. In humans, Cr(VI) neurotoxicity can differ across age groups. Childhood exposure is linked to autism spectrum disorder or attention deficit hyperactivity disorder, whereas adult exposure is linked to olfactory dysfunction, memory loss, polyneuropathy, and motor neuron disease [10; 32; 33; 34; 35; 36; 37; 38]. Cr is reported to accumulate in the brains of non-occupationally exposed individuals, with the highest levels reported in the temporal cortex and pituitary gland [39]. Notably, older individuals exhibited higher Cr levels in brain tissues, suggesting Cr accumulates in the brain with age or that geriatric individuals accumulate more Cr in the brain upon exposure [39]. Animal studies report Cr(VI) neurotoxicity following injection, inhalation, or drinking water exposure and across multiple taxa (fish, birds, mammals, _Drosophila_) [39].