Question: exposure to what caused the town that is now Route 66 State Park to be evacuated?

Context articles: Angel Delgadillo
West Tyson County Park
Route 66 State Park
Route 66 Park
U.S. Route 66 in Missouri
Arizona State Route 66
U.S. Route 66 in Arizona
Times Beach, Missouri
Paris Springs Junction, Missouri
U.S. Route 66 in California

Angel Delgadillo is a businessowner in Seligman, Arizona who has been dubbed the 'guardian angel' of U.S. Route 66.
 He is the main founder of the Historic Route 66 Association of Arizona, established in 1987 to campaign for "Historic Route 66" signage on the former US highway; similar initiatives have since been established in every U.S. Route 66 state.
West Tyson County Park is a county park in the U.S. state of Missouri consisting of 673 acres located in St. Louis County east of the town of Eureka.
 The park is located north of Interstate 44, west of Tyson Research Center, east of Route 66 State Park, and south and east of the Meramec River.
Route 66 State Park is a state park in the U.S. state of Missouri, located on the former site of the town of Times Beach.
 It is a 419 acre park located less than 1 mi east of Eureka.
Route 66 Mural Park (opened 2013 in Joplin, Missouri) operates as a public park, specifically as a touchstone for US Route 66 tourists as well as for local preservers of U.S. Route 66 in Missouri.
 The park includes two large tile murals proposed by Paul Whitehill, produced by Images In Tile USA and designed by artists Chris Auckerman and Jon White.
 The park also features a bifurcated red sports car that anyone on pilgrimage can slide up beside and have a quickie photograph taken.
 Close to the intersection of 7th Street and Main, the mural covers the south side of Pearl Brothers, the iconic green hardware store of downtown Joplin.
 Near that same intersection, US Route 66 once shifted west and headed into Kansas.
U.S. Route 66 (US 66, Route 66) is a former east–west United States Numbered Highway, running from Santa Monica, California to Chicago, Illinois.
 In Missouri, the highway ran from downtown St. Louis at the Mississippi River to the Kansas state line west of Joplin.
 The highway was originally Route 14 from St. Louis to Joplin and Route 1F from Joplin to Kansas.
 It underwent two major realignments (in the St. Louis and Joplin areas) and several lesser realignments in the cities of St. Louis, Springfield, and Joplin.
 Current highways covering several miles of the former highway include Route 100, Route 366, Route 266, Route 96, and Route 66.
 Interstate 44 (I-44) approximates much of US 66 between St. Louis and Springfield.
State Route 66 (SR 66) is a surface road in the U.S. state of Arizona in Mohave and Coconino Counties.
 In 1914, the road was designated "National Old Trails Highway" but in 1926 was re-designated as U.S. Route 66.
 In 1985, U.S. Route 66 was dropped from the highway system.
 Parts of the highway were either absorbed into I-40, turned over to the state (SR 66), or turned over to Yavapai County.
U.S. Route 66 (US 66, Route 66) covered 401 mi as part of a former United States Numbered Highway in the state of Arizona.
 The highway ran from west to east, starting in Needles, California, through Kingman and Seligman to the New Mexico state line as part of the historic US 66 from Santa Monica, California, to Chicago, Illinois.
 The highway was decommissioned in 1985, although portions remain as State Route 66 (SR 66).
Times Beach is a ghost town in St. Louis County, Missouri, United States, 17 mi southwest of St. Louis and 2 mi east of Eureka.
 Once home to more than two thousand people, the town was completely evacuated early in 1983 due to a dioxin contamination that made national headlines.
 It was the largest civilian exposure to dioxin in the country's history.
Paris Springs Junction is a small unincorporated community in Lawrence County, Missouri, United States.
 It lies along former U.S. Route 66 (now a county road west of the junction of Route 266 and Route 96), four miles (6 km) west of Halltown.
 Paris Springs Junction started as a few business on Route 66 and, with the decommissioning of that highway, has now become only homes.
 It was so named because of a former town named Paris Springs to the north.
 That town was founded in 1855 and survived until the time of Route 66's decommissioning.
U.S. Route 66 (US 66, Route 66) is a part of a former United States Numbered Highway in the state of California that ran from the west in Santa Monica on the Pacific Ocean through Los Angeles and San Bernardino to Needles at the Arizona state line.
 It was truncated during the 1964 renumbering and its signage removed in 1974.
 The highway is now mostly replaced with several streets in Los Angeles, State Route 66 (SR 66), Interstate 15 (I-15) and I-40.