Sources and Impacts of Selenium Contamination
13
conditions prevalent in arid climates and are carried in solution in the
drainwater (Presser and Ohlendorf 1987).
When subsurface irrigation drainage is discharged into surface waters, a variety of serious biological effects can take place. The immediate impact is degradation of surface and groundwater quality through
salinization and contamination with toxic, or potentially toxic, trace
elements (selenium, arsenic, boron, molybdenum, chromium, etc.).
Long-term impacts can occur if selenium enters aquatic food chains. A
landmark case of this type of impact occurred in 1985 at Kesterson
National Wildlife Refuge, CA, in the United States (Table 1.2, Figure
1.1), where thousands of fish and waterfowl were poisoned. Selenium
and other trace elements were leached from soils on the west side of
the San Joaquin Valley and carried to the refuge in irrigation return
flows that were used for wetland management (Zahm 1986). Selenium bioaccumulated in aquatic food chains and contaminated 500 ha
of shallow marshes. Elevated selenium was found in every animal
group inhabiting these wetlands, from fish and birds to insects, frogs,
snakes, and mammals (Saiki and Lowe 1987; Clark 1987; Ohlendorf et
a1. 1988). Selenium-induced reproductive impairment was documented
in a variety of species, and teratogenic deformities (a biomarker of
chronic selenosis) were evident as well (see Chapter 3). Congenital
malformations in young waterbirds were severe and consisted of missing eyes and feet, protruding brains, and grossly deformed beaks, legs,
and wings (Ohlendorf et a1. 1986a, 1986b, 1988; Hoffman et a1. 1988).
Several species of fish were eliminated, and a high frequency (30%)
of stillbirths occurred in the single remaining species (Saiki and Ogle
1995). Laboratory studies conducted by the US Fish and Wildlife Service confirmed the field assessment that irrigation drainage was the
source of elevated selenium and toxic effects (Lemly et a1. 1993).
The biogeochemical conditions leading to the production of seleniferous subsurface irrigation drainage, culminating in death and deformities in wildlife, have been termed the "Kesterson Effect" and are
prevalent throughout the western United States (Presser 1994; Presser
et a1. 1994; Seiler et a1. 1999). These conditions include: (1) a marine
sedimentary basin that contains soils formed during the Cretaceous
period, which have relatively high natural concentrations of selenium;
(2) alkaline, oxidized soils that promote the formation of water-soluble
forms of selenium (especially selenate); (3) a dry climate, in which
evaporation greatly exceeds precipitation, leading to salt buildup in
soils; (4) subsurface layers of clay that impede downward movement
of irrigation water and cause waterlogging of the crop root zone; and
(5) subsurface drainage into wetlands and aquatic habitats by natural
gradient or buried tile/pipe drainage networks. In view of the key factors that contribute to hazardous subsurface drainage, it is important
13
conditions prevalent in arid climates and are carried in solution in the
drainwater (Presser and Ohlendorf 1987).
When subsurface irrigation drainage is discharged into surface waters, a variety of serious biological effects can take place. The immediate impact is degradation of surface and groundwater quality through
salinization and contamination with toxic, or potentially toxic, trace
elements (selenium, arsenic, boron, molybdenum, chromium, etc.).
Long-term impacts can occur if selenium enters aquatic food chains. A
landmark case of this type of impact occurred in 1985 at Kesterson
National Wildlife Refuge, CA, in the United States (Table 1.2, Figure
1.1), where thousands of fish and waterfowl were poisoned. Selenium
and other trace elements were leached from soils on the west side of
the San Joaquin Valley and carried to the refuge in irrigation return
flows that were used for wetland management (Zahm 1986). Selenium bioaccumulated in aquatic food chains and contaminated 500 ha
of shallow marshes. Elevated selenium was found in every animal
group inhabiting these wetlands, from fish and birds to insects, frogs,
snakes, and mammals (Saiki and Lowe 1987; Clark 1987; Ohlendorf et
a1. 1988). Selenium-induced reproductive impairment was documented
in a variety of species, and teratogenic deformities (a biomarker of
chronic selenosis) were evident as well (see Chapter 3). Congenital
malformations in young waterbirds were severe and consisted of missing eyes and feet, protruding brains, and grossly deformed beaks, legs,
and wings (Ohlendorf et a1. 1986a, 1986b, 1988; Hoffman et a1. 1988).
Several species of fish were eliminated, and a high frequency (30%)
of stillbirths occurred in the single remaining species (Saiki and Ogle
1995). Laboratory studies conducted by the US Fish and Wildlife Service confirmed the field assessment that irrigation drainage was the
source of elevated selenium and toxic effects (Lemly et a1. 1993).
The biogeochemical conditions leading to the production of seleniferous subsurface irrigation drainage, culminating in death and deformities in wildlife, have been termed the "Kesterson Effect" and are
prevalent throughout the western United States (Presser 1994; Presser
et a1. 1994; Seiler et a1. 1999). These conditions include: (1) a marine
sedimentary basin that contains soils formed during the Cretaceous
period, which have relatively high natural concentrations of selenium;
(2) alkaline, oxidized soils that promote the formation of water-soluble
forms of selenium (especially selenate); (3) a dry climate, in which
evaporation greatly exceeds precipitation, leading to salt buildup in
soils; (4) subsurface layers of clay that impede downward movement
of irrigation water and cause waterlogging of the crop root zone; and
(5) subsurface drainage into wetlands and aquatic habitats by natural
gradient or buried tile/pipe drainage networks. In view of the key factors that contribute to hazardous subsurface drainage, it is important