Cattle-Fever Tick Eradication in Florida and a Legacy of Arsenic Contamination R. Dean Rhue Soil and Water Science Department University of Florida Cattle Dip Vats Ticks introduced into FL in 16 th century by Spanish settlers Ticks carried disease later known as Cattle Fever or Bovine Babesiosis Ticks spread throughout southern US and Mexico Southern cattle carried the ticks and Cattle Fever north during cattle drives, infecting northern herds and resulting in hundreds of dead cows along the way Cattle Dip Vats (cont d) Southern cattle had to be treated to kill ticks before being transported or driven into clean areas nly known tickicide prior to WWII was arsenic (post WWII, DDT and toxaphene were used) Fl was open range till about 1945 Cattle rounded up and driven to nearest dip vat Wanted vats spaced across the state so that no cattle would have to be driven more than 3 to 5 miles to a vat site ~3200 dip vats in FL Cattle Tick Eradication Program 1917 Fla passed local option law 1923 Fla passed mandatory law 1930 Eradication began in Alachua Co. 1937 Tropical tick arrived in S. Fla; Eradication program stalled 1940 to 1960 Sporadic outbreaks occurred across the state 1962 Fla declared tick free for last time! 4' Cattle Dip Vat 26' Drip Pad Vats held ~1500 gallons of solution. When freshly charged, the concentration was about 1500 mg (III)/L. ver time the solution levels would drop and the (III) would oxidize to (V). Solutions would be recharged with additional (III) to maintain potency. Each spring, the vats were emptied, cleaned out, and refilled with fresh solution. A common method of disposing of the old solution was to dig a pit adjacent to the vat and pump the solution into the pit, where the solution will soak into the ground and do not harm. 1
Dudley Farm Vat Jackson Gap Vat US 441 Vat Tus Vat Inorganic Arsenic Chemistry (III) (V) wen Vat Wll Wellons Vat Vt Arsenous Acid Arsenite Arsenic Acid Arsenate rganic Arsenic Chemistry Trimethyl Arsine H H H Arsine Trimethyl Arsine xide Acid Dissociation Constants for Arsenous and Arsenic acids pk 1 pk 2 pk 3 (III) 9.2 14.2 19.2 (V) 2.2 6.9 11.5 Predominant forms of (V) in soils and aquatic systems is H 2 4 - and H 4 2-. The predominant form of (III) is H 3 3. 2
(V) reacts predominantly with amorphous oxides of Fe and Al in soils. Metal oxides have hydroxyl ions on their surfaces which can react with by a process known as ligand exchange. Surface Hydroxyl Monodentate - H 2 4 - Bidentate, Binuclear - - H 4 2- Bidentate, Mononuclear In order for (V) to adsorb to Fe or Al oxide it must first deprotonate to form the appropriate anionic species: H 2 4 - for a monodentate complex or H 4 2- for a bidentate complex. But because of its pk a s, these two forms of already exist in the environment. In contrast, H 3 3 doesn t deprotonate until around ph 9 and therefore doesn t react as strongly with Fe and Al oxides in soils The more strongly an anion adsorbs the less mobile it is in the environment. Thus (III) tends to be much more mobile in soil and aquatic systems than (V). The amount of amorphous Fe and Al oxides in soils generally increases with its clay content. Thus absorption generally increases with clay content. Adsorption is quantified using an adsorption isotherm: The mobility of a substance in soil is quantified using the concept of retardation, R: Slope = K d R = 1 + ( / )K D where is bulk density, is volumetric water content, and K D is the slope of the sorption isotherm No sorption, K D = 0, R = 1; examples include N 3 and Cl Solution Conc 3
Since A(V) adsorbs more strongly than (III), its K d is greater and, therefore, its retardation is greater. In addition to clay content, the mobility of in soil beneath a dip vat will also vary from site to site due to factors such as ph, aeration, and drainage. These factors will affect the depth and lateral distance that has moved away from a dip vat during the 80 or so years since the initiation of the tick eradication program. Quick n-site Field Test for Arsenic Acid Solution + Zn = H 2 H 2 + (III) or (V) = Arsine (H 3 ) Bison Pen Vat Paynes Prairie A Horizon, sand Bison Pen Vat Site Millhopper Series Grossarenic Paleudult E Horizon, sand Bt Horizon, sand Bison Pen Vat Bt A and E Hawthorne Clay Plume Paynes Prairie Entrance Road, Paynes Prairie Visitor Center 4
A Horizon, sand Paynes Prairie, South Rim Visitor Center Site Tavares Series Typic Quartzipsamment 8-9' of Sand C Horizon, sand Sandy clay Sink Hole A Horizon, sand Williston Road Vat Site E Horizon, sand Pottsburg Series Grossarenic Alaquod Bh1 Horizon, sand Williston Road Vat Bh2 Horizon, sand Williston Road Vat Williston Road Vat 100 m B h Groundwater 100 m Vat Paynes Prairie 0 20 40 60 80 100 ppm 5
Dudley Farm Vat A Horizon, f. sand E Horizon, f. sand Bt1 Horizon, f. s. loam Dudley Farm Vat Site Bonneau Series Arenic Paleudult Bt2 Horizon, s. c. loam Btg Horizon, c. loam 6