Reviews of Environmental Contamination and Toxicology Volume 223

Breathable air is a gas mixture made up of 78 % nitrogen, 21 % oxygen, and 1 % carbon dioxide and other gases such as argon, radon, and xenon (Pani 2007). Atmospheric contamination is the presence in the air of substances that change its chemical and physical characteristics. Air pollution derives primarily from fossil fuel combustion products that are emitted into the air. In some areas, the effects of air pollution are exacerbated when climatological and geographical factors restrict its dissipation. Over the past decades, the air quality of many urban centers has seriously deteriorated. As a result, millions of people are exposed to pollution levels above the recommended limits by the World Health Organization (WHO), such as indicated by the United Nations Environment Programme. Air pollution is currently a concern in the American region, wherein several capital cities have levels that exceed national and international guideline limits. Such is the case for Santiago, the capital city of Chile, which is among the cities with higher air pollution levels in the world (Ostro 2003). The location of Santiago and the weather it experiences, when combined with high anthropological emissions, create critical air pollution conditions. The interaction of air pollution and heat can impair the health and well-being of people, particularly the elderly and children (Kinney 2008).

Rapid industrialization and modernization around the world have produced the unfortunate consequence of releasing toxic wastes to the environment. Metal pollutants are derived mainly from industrial and agricultural activities. The former includes activities such as waste disposal, chemical manufacturing, and metal pollutants from vehicle exhaust, and the latter involves activities such as the use of agrochemicals, long-term application of sewage sludge, and wastewater to agricultural soils. Such releases have adversely affected human health and have produced toxic effects on plants and the soil microorganisms associated with them. Toxic metal contaminants from wastes or other products accumulate in the agricultural soils to which they are applied, threaten food security, and pose health risks to living organisms by their transfer within the food chain. Once heavy metals reach the soil, they are absorbed by plants and may be taken up by animals and humans through consumption of contaminated food or drinking water. They may even be inhaled as particulate contaminants, and due to their persistent nature, they may accumulate in both plants and animals over time.

Mercury (Hg) is a globally distributed environmental contaminant with both natural and anthropogenic sources. Of the forms and oxidation states of Hg, the organic form, methylmercury (MeHg), is the most biologically available and the most toxic (Scheuhammer et al. 2007). MeHg can be neurotoxic, embryotoxic, and can impair physiological function, particularly by disrupting endocrines (Tan et al. 2009) and altering reproductive behavior (Frederick and Jayasena 2010). Because MeHg can be bioaccumulated and biomagnified through the food web, diet is the major pathway by which vertebrates are exposed (Liu et al. 2008). Species occupying the higher trophic levels in aquatic systems are considered to be at the greatest exposure risk, particularly the birds at trophic levels 4 or 5. Although concentrations of Hg may exist in surface water at or near only historical background levels, the concentrations of Hg that exist in wildlife are higher (Liu et al. 2008). Chronic dietary exposure to relatively small, environmentally relevant concentrations of MeHg is sufficient to be accumulated by tissues to concentrations that impair reproduction of birds (Frederick and Jayasena 2010).

Engineered nanomaterials are increasingly employed in a variety of applications. The size of nanoparticles, by definition, ranges between 1 and 100 nm in at least one dimension (The Royal Society and The Royal Academy of Engineering 2004). Such dimensions result in a high surface area to volume ratio. The subsequent chemical, physical, and biological properties of nanomaterials are unique, and lead to diverse technical applications and prospectively to widespread use in commercial products. In 2004, the production volume of nanomaterials was estimated to be 2,000 t worldwide, and is expected to rise to 58,000 t within the next decade (The Royal Society and The Royal Academy of Engineering 2004).

Diazinon (O,O-diethyl O-2-isopropyl-6-methylpyrimidin-4-yl phosphorothioate) was first registered in the USA in 1956 (US EPA 2006) by the Swiss company J.R. Geigy. Diazinon is a broad-spectrum contact organophosphorus pesticide that is used as an insecticide, acaricide, and nematicide. Diazinon has been widely used to control soil and foliage insects and pests on a wide range of crops such as rice, fruits, wine grapes, sugarcane, corn, and potatoes. Diazinon is also used to control mange mites, ticks, lice, biting flies on sheep, cows, pigs, goats, and horses. In California, diazinon has been applied primarily on fruits, vegetables, and for landscape maintenance and structural pest control. In 2010, a total of only 64,122 kg of diazinon was used in California (CDPR 2010a). Diazinon was formerly used in household and garden products for pest control. However, manufacturing of indoor use products was discontinued on June 30, 2001, and production of nonagricultural outdoor use products containing diazinon was discontinued on June 30, 2003. As of December 31, 2004, sales of diazinon-containing products for residential use ceased (US EPA 2000), resulting in diazinon falling to a rank of 94 among the most used pesticides in California by 2010 (CDPR 2010b). Diazinon is formulated as a wettable powder, granules, liquid concentrates, seed dressings, microencapsulations, and impregnated materials (US EPA 2006). Some typical formulations containing diazinon as an active ingredient (a.i.) include the following: Basudin® 10 (10 % a.i.), Knoxout® (Pennwalt, 23 % a.i.), Nucidol® 60 (60 % a.i.), Alfatox®, Gardentox®, and several other trade-named products. Although concentrations have decreased nationwide in urban waters, diazinon is still frequently detected as a residue in agricultural watersheds. In California’s agricultural regions with the highest diazinon use, the detection frequencies in 2005–2010 could reach 90 % of the monitoring samples; moreover, the exceedance rate vs. the water quality criterion of 0.1 μg/L was 66.7 % (Zhang and Starner 2011). This large proportion of detections and exceedance of water quality criteria have led to concerns about diazinon’s potential environmental impacts. In this chapter, we provide a review of the environmental fate of diazinon and describe its toxicity to aquatic organisms.