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<br />rcore:rnediacion of Se.laden soils. 'Terry and
<br />'h),\ resear~ ATOUP arc' currendy crying to
<br />ctJOOUU Q>ysiological, biochemical,
<br />and mtcrobtal"'mechanisms involved in
<br />the volatilization process in order to pro.
<br />vide new ways to accelerate the volaciliza. ,
<br />cion races in planes.
<br />The usc of Sc voladlizadon for Se rc-
<br />maval from soils and waters is attractive:
<br />because, in ,his approach, Se is complc,e1y
<br />removed from the ecosystem, making jt
<br />non-detrimental, reducing the risk of
<br />emry of Se in,o rhe food chain (Banuelos
<br />and Meek 1989) and, the release of large
<br />amounts of volatile Se (dimerhylsdenide;
<br />OMSe) into thc armosphere. Toxicologi-
<br />cal studies (Gamher ec al. 1966; Wilber
<br />1980) indicared ,hac OMSe is 500 to 700
<br />dmes less toxic co cars chan inorga-nic Se.
<br />
<br />Water management's role in
<br />phytoremediation
<br />
<br />Optimum management practices must
<br />be identified and used at the respective
<br />Sc-Iaden sice in order for phyroremedia-
<br />rion co be successfu1. To' this end, water
<br />management strategies are instrumental in
<br />growing Se-accumularing plants for phy-
<br />coremediacion in Se~laden soils in irrigat-
<br />ed regions for cwo principal reasons: co
<br />a;;hj<.:.;~ ,he greatest production of biomass
<br />with the minimum application of irriga-
<br />cion wacer and, thus, produce a. minimum
<br />of drainage Water; and to minimize perco-
<br />ladon losses or surface run~off of Se-Iaden
<br />effiuenc. Optimum races of water applica-
<br />cion for species grown for phytoremedia-
<br />cioo, Le., Brassiea, are unknown. Banuelos
<br />and Hucmachu of the Water Manage-
<br />ment Research Laboratory in Fresno, Cal.
<br />ifornia are curr<:ndy developing crop coef-
<br />ficiems (crop evaporranspiracion relative
<br />
<br />to reference evaporation; used to deter-
<br />mine plane water requirements) for planes
<br />used in phycoremediarion of Se using
<br />,weather data from ,the California Irriga.
<br />tfon Management Information System
<br />(CIMIS) and soil wa<er daca under differ-
<br />ent irrigation regimes. They are invesd~
<br />gating the relationship bc,ween the
<br />amounr of water applied and biomass
<br />producrion in multi.year field studies.
<br />Providing [he plant enough wacer for op-
<br />timal growth while minimizing dcep pcr-
<br />colation losses not only reduces the pro-
<br />duction of effluent to dispose of, but che
<br />greater bioma.ss yields should result in
<br />more soil Se removed by the plantS and
<br />possibly more volatilization of Se.
<br />Determining water requirements of
<br />plant species used for phycoremediation
<br />and only applying warer ,he planr necds
<br />in a specific soil should noe contribute co
<br />the producdon of excessive Se.laden effIu.
<br />ent. Moreover, over-irrigation in crops
<br />used for phytoremediadon may promote
<br />anaerobic conditions that increase the
<br />transformation of selenate to more: re-
<br />duced species of S~ chac are not easily
<br />available for plam uptake (Ncal and Spos-
<br />iro 1991) but are "ill available for leach-
<br />ing, decreasing rhe efficiency of phyrore-
<br />mediation.
<br />
<br />Disposal options for plants
<br />used in phytoremediatlon
<br />
<br />Plant species used for phytoremedia.
<br />cion in Se~rich soils may not only mjni~
<br />mize the Seload cvenrually residing in
<br />agricultural effluent by phytoremediation,
<br />but the plane species as pare of a crop ro.
<br />tation may become a product of econom-
<br />ic importance for the grower. In this re-
<br />gard, harvesred plam macerialladen wirh
<br />
<br />Table 4. Crude protein (CPl, digestible dry matter (DOM), and selenium (Sa) content In
<br />different species grown in so/l enriched with Se.laden plant material
<br />CP' DDM'
<br />(0/0) (0/0)
<br />
<br />Plant species"
<br />
<br />So'
<br />(mgkg")
<br />
<br /> Clippings 1
<br />Tall fescue 19a' 92a 1.3 (.05)a
<br />Alfalfa 22ab 93. 4.7 (.04)b'
<br />Birdsfoot Ir~loil 19a 92a 3.1 (.06)b'
<br /> Clippings 2
<br />Tall fescue 16a 93a 1.5 (.06)a
<br />Alfalfa 24b 94a 10.6 (.07)b'
<br />Blrdsfoot trefoil 17a 93a 4.7 (.07)c'
<br />
<br />. Harvested mustard (Brl1.Jslca jU1/.((a (um L.) plane tissues containing: (250 mg So:: kg" dry matter) were incorpo-
<br />rated into the $oil at 375 g Se ha" (Banuelos et 1.1. 1993b)
<br />'Composite sal1'lple: feom nine: repliC1cions
<br />'Mean values from nine replicacions. Value within parenthesis represents the coefficient ofv;;riadoo
<br />'Mean separation in columtlS by Duncan's multiple range test. The same letters represent no signific:uH difference
<br />betweeen tte:1ements at the p < 0.05 level
<br />'VrtJues exceed ,he recommended Se concencr::r.cions for livestocl: feeding
<br />
<br />Se can be carcfully blended wi,h animal
<br />forage, such as alfalfa and feed, for ani-
<br />mals in surrounding areas where Se dd'i-
<br />dency is a problem. Selenium, while not
<br />required by planes, is an essencial crace e1~
<br />ement for adequare nuuition and health
<br />for mammals (Se deficiencies are proba-
<br />bly a greaeer problem than Se toxicities in
<br />animals, Le., ease side of ceneral Califor..
<br />nia). Gencrally, dices comaining 0.1-0.3
<br />mg Se kg-' (ppm) wi11 provide adequare Se
<br />for animal feed (Mayland 1994). Animal
<br />producers wishing to ensure adequate
<br />supplies of Se to their livestock have a va~
<br />riery of cechniques at rheir disposal, which
<br />includc giving Se by injecrion or by
<br />moueh as a feed supplement. Anoeher
<br />means of improving che Se scatus of ani-
<br />mals is to add the material [0 soils as a
<br />source of organic Se fertilizer for such for-
<br />age planes as alfalfa, birdsfoot crefoil, or
<br />taU fescue. In this way, animals may seill
<br />eat forage species without any blended
<br />planr matcrial (planes used for phycoreme-
<br />diarion), yet the forage species will absorb
<br />Se. Table 4 shows the accumularion of Se
<br />and nutritional value in pOtencial forage
<br />crops grown in soil with incorporared Se-
<br />laden plant material used previously for
<br />phycoreme:diadon.
<br />Ocher disposal possibiliries for Se-Iaden
<br />plane material include its use in produc~
<br />tion of paper products or utilizaeion as
<br />fuel for biogeneration power plants. The
<br />latter opeion must be considered if con~
<br />centracions of eoxic trace metals (i.e., Cd.
<br />As) found in rhe planr marcrial exceed
<br />concentrations considered environmental..
<br />Iy safe for animal consumption (Narional
<br />Research Council 1980). Oil cxrracced
<br />from seed of BraJIica species grown for Se
<br />phycoremediacion under Se-Iand field
<br />conditions is presently being evaluated for
<br />ics qualiry (Banuelos 1997).
<br />
<br />Future directions
<br />
<br />The high COStS associated wieh environ~
<br />mental remediation of Se is causing many
<br />scare, federal, and local agencies to look to
<br />lower cose alternatives. Phycoremediacion is
<br />a potentiallow-cose cechnology urilizing the
<br />plants' abiliey to influence physiological, bi-
<br />ological, and chemical processes within the
<br />plant and within rhe plants rhizosphere char
<br />remediare Se.laden soils. Research in rhe
<br />developmenral phases of phycoremediarion
<br />has shown its potencial for succesS. Based
<br />on che limired number of conducted stud-
<br />ies, plane species that can be effective for
<br />the phycoremediation of Se should have as
<br />many of the following characrerisrics as
<br />possible:
<br />. faSt growth rare;
<br />. high biomass pro~uccion;
<br />
<br />~OVSM8ER.DECEMBER 1991 429
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