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Abrupt decrease of lead concentration in the Mediterranean sea: A response to antipollution policy

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Abrupt decrease of lead concentration in the Mediterranean sea: A response to antipollution policy
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  GEOPHYSICAL RESEARCH LETTERS, VOL. 21, NO. 19, PAGES 2119-2122, SEPTEMBER 15, 1994 Abrupt decrease of lead concentration n the Mediterranean sea: A response o antipollution policy E. Nicolas and D. Ruiz-Pino Laboratoire e Physique t Chimie Marines, nive•itd Pierre t Marie Curie, CNRS/1NSU, illefranche, rance. p. Buat-M6nard D6p•ement e G6ologie t Oc6anographie, RA CNRS 197, Universit6 e Bordeaux , France. J.P. Bethoux Laboratoire e Physique t Chimie Marines, Universit• Pierre et Marie Curie, CNRS/INSU, Villefranche, rance. Abstract. In the Northwestern Mediterranean basin, lead concentrations n the surface waters have halved over the last 10 years. his decrease ollowed uccessive imitations f the use of lead additives n gasoline occurred n European ountries ince 1976 and he progressive se of unleaded uel. The evolution of lead concentration n the Mediterranean waters s simulated by using a geochemical six-box model and validated by measurements ade since 1983. In this way, it is demonstrated that: ) previous major pollution was essentially ead gasoline derived; i) international ntipollution olicy s efficient; ii) the Mediterranean ea is an important case study area to assess he marine iosphere's esponse o environmental hanges. Introduction During he last decade, t became ncreasingly vident hat the atmosphere s the major pathway or pollutant ead nput o the oceans Boyle et al.. 1986]. In the mid-1960s, most of the lead anthropogenic ischarge nto he atmosphere riginated rom he use of alkyl-leaded gasoline Pacyna, 1984; Pattenden nd Branson, 987; Hopper et al., 1991] and ead distribution n the upper waters of the Western North Atlantic was determin6d y North American ndustrial nputs. This was evidenced by the decline in the surface lead concentration observed in the North Atlantic Ocean since 1979, a result of the rapid decline of leaded gasoline onsumption n the U.S., beginning round ear 1970. n the Mediterranean ea, atmospheric ead is primarily derived from European missions Arnold t al., 1982; Dulac et al., 1987; Maring t al., 1987]. High Pb concentrations easured n the surface aters of the Western Mediterranean uring he 1980's were explained by a non-steady tate caused by increasing atmospheric nput since 1960 [Ruiz-Pino t al., 1990; Bethoux t al., 1990a]. n the Northwestern urope, he use of unleaded gasoline as been widely spread or several years but, in Southwestern nd Eastern urope, b additives re still n use, t least partially. Marine lead concentrations btained n the Northwestern Mediterranean basin from 1983 to 1992 allow an evaluation f the chemical esponse f the Mediterranean ea o :hanges f ead nputs rom atmosphere ollowing he European policy nitiatives oncerning ead dditives n gasoline. Copyright 994 y the American eophysical nion. Paper umber 4GL01277 0094-8534/94/94GL.01277503.00 Data and Modeling Apart rom a first historical measurement n 1963 Tatsumoto nd Patterson, 963], o eliable measurements f lead were acquired concerning he Mediterranean ea until the 1982 Phycemed Program Copin-Montggut t al., 1986]. Until then, contamination problems lagued oth sampling nd analysis f lead. This study uses the Phycemed measurements and those from French oceanographic Intersite" 1984)and "Medatlante" 989)cruises as well as those obtained since 1987 at "Dyfamed" station, a permanent site of the JGOFS-France program, in the Northwestern asin, 30 miles offshore Nice [ Fowler et al., 1987]. During the Phycemed 1983) and Medatlante (1989) cruises, samples ere measured mmediatly n board y anodic tripping voltammetry Laumond et al., 1984]. The general analytic procedure s summarized as follows: each sample was systematically nalysed n each of the wo cells of the analytical stand ntil he difference etween wo independant easurements is of the magnitude f the detection imit (14 pmol). The same procedure as applied o the ntersite 1984) and he Dyfamed 987 samples, hich were analysed n a class 100 clean oom at the ashore aboratory. A new strategy as adopted n 1988, or the Dyfamed program, in order o avoid hat expected oncentration hanges e hidden by random ontamination f the samples. t each depth, samples were systematically ollected rom three distinct GOFLO bottles. At the ashore laboratory, random lead determinations were conducted according to the above analytic method and, consequently, or each depth, data in Table I (columns , g, h and ) result rom at least six measurements. Since 990, lead concentrations have decreased n surface waters at Dyfamed station Table 1). We analysed his decrease long with historical data obtained n the Northwestern Basin, where vertical ead profiles rom 1983 o 1988 show high concentrations in the surface waters and relatively ow and homogeneous concentrations elow 300 m (Figure 1, left side). Later profiles, from 1991 and 1992 (Figure 1, right side), are nearly uniform throughout he whole water column, while surface concentrations have dropped o less han half of the 1983-1988 values. Is the decrease of lead observed in the Western Mediterranean Basin a direct result of the phasing out of European eaded gasoline? he use of Pb additives iffers mong he European Community EC) members. uring he 1980's, he proportion f unleaded asoline epresented 9% of the fuel consumption n 2119  2120 NICOLAS ET AL.' RESPONSE TO ANTIPOLLUTION POLICY Table 1. Lead oncentrations pmol b kg l ) in the North-Western editerranean ea nd tandard eviations. Phycemed tation, Oct., 1983 43ø05N, 8ø00E); Intersite tation, ept., 984 43ø00N, 8ø00E); (Jun., 98'•). (Oct., 987), (Jun., 988), (Oct., 1990), (Jan., 991), (Apr., 1992) Dyfamed tation 43ø25N, 7ø52E); Medatlante tation, an., 989 40ø00N, 6ø00E). Depth m a b c d e f g h i 10 382 367 309 415 411_+17 238_+14 159-• 154+_10 20 288 266 222.+. 2 266 238__+10 169-+8 203+ 4 30 295 213+24 177_+12 64+13 155__+13 50 256 237 232 246 98+__5 213 157+11 169+16 189+__24 75 198 179-+10 227 158-+10 192-+17 83__+10 100 242 193 188+__.26 204 42+12 164+10 170-•__15 500 155 130 179 174 155+14 155 118-+12 118+__5 126+12 1000 142 179 184 122 119+__1 124:: :9 112-+8 1500 128 126 174 145 116-+11 155+10 Surface ayer, mean alue 10-100 m) 284-+67 302-+92 263-+35 285__+116 235+__88 228+___27 185+__43 170-+12 176+__20 Deep ayer, mean value 500-1500 m) 142+14 128+__3 77+___3 179 -__7 155 141+_17 119•__1 119-+4 131+__22 Germany, 1% in the Netherlands, 4% in UK, 8% in France nd less han 1% n Italy and Spain Hebners, 991]. Lead ife time n the atmosphere s very short, nly a few days Remoudaki t al., 1991] and, in the Western Basin, more than 50% of the lead inputs come from adjacent countries Dulac et al., 1987]. Consequently, n a first approximation, he evolution of lead consumption n France may be a good ndicator f the ead nput into the Northern Mediterranean. Figure 2 shows lead consumption n the French production f alkyl-leaded asoline (Paul Tepik, Union Franqaise es ndustries 6troliires, ersonal communication). onsumption ncreased rom 1950 to 1976 at a rate of about 9-10% a year, following the general economic expansion. he 1973-1974 break s due o the first oil crisis nd, between 1976-1981, the decreasing rend occurred after the first legal estrictions orcing ead concentrations n gasoline o drop from 0.64 to 0.4 g 14. Then n 1988, second brupt hange I • raw ,%?,,,,,• ,,,.,,:,,.,,.,,,,,. sw) I I W SiN EAtITE;FI N BASIN SIClILY • TI:IAITS Eigure 1. Vertical rofiles f lead concentrations easured n the Nothwes[ern Mediterranean, n 1983 and 988 (leœt ide) and in 991 and 1992 (right side). resulted n even ess ead used n leaded asoline 0.15 g 1 • in 1991), as well as the expanded se of unleaded asoline 30% n 1992). Subsequent o the implementation of European regulations, ead concentration ecreased etween 1987 and 199 in aerosols and in rainwater both at Monaco [Marmenteau et Veglia, 1992] and at Cape Ferrat[ Migon et al., 1993]. In order to simulate recent trends in marine concentrations, we used a simple geochemical on-steady ix-box model previously developed or the Mediterranean ea o explain race metal data obtained uring he Phycemed 1983 cruise Bethoux t al., 1990a; Ruiz-Pino et al., 1991]. This model (Figure 3) takes into consideration: ) water exchanges with the Atlantic Ocean; ) external nputs, .e., portions f dissolvable ead in atmospheric inputs Aw in the Western Basin and Ae in the Eastern Basin); ) vertical transfers ia circulation and water mixing, as well as biological ransfers w and Fe; 4) sedimentation w and Se n Western nd Eastern asin, espectively. sing measured arine concentrations, he model stimates he otal external nputs and the role of each process biological r physical) n the ead cycle. Also, it predicts the evolution of surface and deep water concentrations, nce having dopted volution rends f the hree functions: xternal nputs, iological ransfers nd sedimentation in the Western and Eastern basins. External inputs, biological ransfers, sedimentation Using he model Figure 3), external nputs n 1983 can be estimated rom measured ead concentrations. he soluble ead inputs rom he Atlantic re estimated o 7.6x10 tool y'• and assumed onstant ver ime. This hypothesis s supported y he relatively weak variation over time of mean measured concentrations est f Gibraltar trait: 46 pmol g in 1981  NICOLAS ET AL.' RESPONSE TO ANTIPOLLUTION POLICY 2121 100 200 300 400 100 200 300 400 0 , I • '•' ' • 0 ]' '- • ' • ' ' (pM/kg) -300 • -300 oot/I .oo] .,oo ;2 -1200]• -1200 1500 -1500 Figure . Lead onsumption n alkyl- eaded asoline n France since 950 P. Tepik, personal ommunication). (Phycemed ruise), 70 pmol g ] in 1985 Lambert t al., 1991a] 155 mol g 1 in 1989 Medatlante ruise). n I983, atmospheric inputs mounted o 21x106 ol -I (Aw= 15 x106 mol -] in he Western asin nd Ae= 6 x10 tool y4 in the Eastern asin, s shown n Table 2). Interbasin differences reflect differences n surrounding ndustrial ctivity and energy consumption. etween 1960 and 1983, the increase f external nputs was estimated o about % a year Bethoux t al., 1990a] This result s comparable to socio-economic ata based n UNEP enquiries United Nations Environment rogratn, 1988] giving annual rowth ates of 1.6% in population, % in energy consumption and 7.5% in total number of cars. The evolution of lead consumption n gasoline (Figure 2), together ith previous alculations oncerning 983 data, allows us to constrain he evolution of atmospheric ources n the Western asin Aw) since 1950 (Table 2). Around the Eastern Basin, ead concentrations n gasoline emain unregulated. Consequently, e have adopted or external nputs here, Ae) a constant ncrease of 6% a year since 1950, based on the 1983 seawater oncentrations Ruiz-Pino et al., 1990]. The inputs n 950 for both basins were calculated o be: Aw + Ae = 4 x 0 6 •nol b -i. Biological ransfer f lead s the esult f biogenically roduced particles inking rom surface o deep waters. Here, we assumed that t is proportional o the new production nd he lead nput evolution. ew production ncreased y 1% per year during 1960-1983. his estimate s based n a 3% a year ncrease n phosphorus urface nputs determined rom concentration change n deep water over the same period, Bethoux 1989]). 15OOO 10000 •. 000 Year 195o 19'56 19'62 19'68 19'74 1g'8o 19'86 1992 Figure 3. General scheme f the six-box model or the Mediterranean ea. Waters, Fluxes (F .... F 0) and lead concentrations C1 ... C 0) are listed in Bethoux eta . [1990a]. Atmospheric ead sources Aw and Ae), lead ransfers hrough biological ctivity Fw and Fe) and edimentation luxes Sw and Se), espectively n the Western nd Eastern asins, re eported in Table 2. Table 2 reports he calculated biological transfer, Fw for the Western Basin and Fe for the Eastern Basin. Sedimentation ates, Sw and Se, are reported n Table 2. For year 1950, values are constrained y the balances, aking nto account lead concentrations n the two opposite lows across he straits of Gibraltar and Sicily. The temporal volution of sedimentation ate is assumed o be proportional o the evolutions f external nputs and biological activity. The estimated sedimentation luxes suggest hat about 50% of the soluble ead delivered at the sea surface since 1950 is buried after being captured by marine organisms. Data-simulation comparison Figure 4 shows imulated ead concentrations rom 1950 to 1992 in surface ayer solid ine) and n deep ayer broken ine) of the Western Basin, obtained by the six-box model. Surface concentrations ollow similar trends as atmospheric nputs (Figure 2). On Figure 4 are also reported ead concentrations measured etween 983 and 1992. A good agreement s obtained between the observed surface concentrations mean values of the 0-100m layer) and the concentrations alculated by the box- model. The abrupt change of lead concentration observed n 1988-1989 s closely simulated y the model and this confirms that the surface ayer responds apidly to changes n external inputs. In constrast, imulated oncentrations n deep water react slowly to changes f surface nputs, simply because he deep water's volume is much greater and so, it dilutes the signal more thoroughly. Since 1950, the regular ncrease f simulated deep water concentrations esult rom a general ncrease f lead nputs in both the Eastern and Western Basins. The first measurement in 1962 [Tatsumoto and Patterson, 1963] is an average of lead concentrations rom 1800 to 2700 m depth, validating the calculated eep concentration n the 1960's. Measurements arried out since 1983 (reported here as the average alue or the 500-1500 m layer) present ome variations, reaching ore r ess 0 x10 12 ool Pb kg ] around he calculated mean oncentration, reater han he expected ensitivity 14x 10' ]2 mol g . They may e inked o peculiarities f he Dyfamed site rather than to analytical difficulties. Dyfamed station s influenced y the Ligurian current, he Levantine ntermediate water circulation, the formation of dense water in winter and the seasonal biological activity. The latter two effects explain most of the variations in the measured le:Jd concentrations. Table 2. Calculate,d alues, n 106 mol b y-l, of atmospheric inputs: Aw and Ae; biological ransfers rom surface o deep layer: Fw and Fe; and sedimentation ates, Sw and Se, for the years 1950, 1983 and 1992 n the Western and Eastern Basins (suffix w and e respectively). he 1983 values or Aw, Ae, Fw and Fe are from Bethoux et al. [ 1990a]. Year Aw Ae Fw Fe Sw Se 1950 3.1 0.9 2.8 2.6 3.7 2.1 1983 17 6 7.6 3.6 12 4.1 1992 6.3 10.1 4.7 3.9 7.2 4.9  2122 NICOLAS ET AL.' RESPONSE O ANTIPOLLUTION OLICY $w==3 74 Sw=I 1.76 I Se=2,12 I Se=4 08 40O.l ..... ' I 10 .,-- 1950 1956 1962 1968 1974 1980 1986 1992 Figure. 4. Evolution f lead concentration n the surface ayer (solid line) and in deep layer (broken ine) of the Western Mediterranean, calculated since 1950 with the six-box model (Figure.3). Measured oncentrations re from 1983 to 1992 (values re n Table 1). The surface oncentrations filled circles) are mean values of 0-100 m data while deep concentrations open circles) are mean values between 500-1500 m. Conclusion The concurrent ecrease f lead consumption n gasoline nd ead concentration in the Mediterranean surface layer clearly demonstrate he previous marine pollution by alkyl-leaded gasoline. ime series measurements n the surface ayer llow ne to track atmospheric hanges f lead cycle n this region nd complete he measured volution of temperature, alinity [Bethoux t al. 1990b] and phosphate oncentration a direct signal f anthropogenic ollution, ethoux 1989]). Moreover, n the six-box model, he response ime of the deep layer o a surface erturbation s about wo centuries efore reaching a new steady-state. Consequently, surface concentration hange n the 70's will begin o be perceptible n deep ayer only wo o hree ecades ater. herefore, program monitoring ead and ts stable sotopes n the air, seawater nd sediments Maring t al., 1987; ambert t al., 1991b; herretl t al., 1992] would provide ight constraints or the deep ayer response nd sedimentation ate. Although, tmospheric ead pollution s a serious roblem or human ealth, t nevertheless provides n unexpected racer xperiment, ransient n nature in the same manner s have anthropogenic missions rom ossil fuel CO , chlorofluorocarbons nd uclear omb est allout). Acknowledgments: e hank r.E. Helmers nd nonymous eferees for useful omments nd L. Alleman or his participation o Dyfamcd 2 experiment; edatlante nd Dyfamed ruises ere upported y France- JGOFS rogram nd his tudy s a contribution o Mast-MTP eodyme subproject MAST 2 CT 93006 ). References Arnold ., A. Seghaier, . Martin, . Buat-Mdnard nd R. Chesselet, G6ochimie de l'a6rosol marin au-dessus e la M6diterran6e Occidentale, I •me J. Etud. Pollutions, .27-37,Cannes, .I.E.S.M., 1982. Bethoux .P., Oxygen onsumption, ew Production, ertical dvection and Environmental volution n the Mediterranean ea, Deep-Sea e&. 5, 769-781, 1989. Bethoux .P., Ph. Courau, . Nicolas nd D. Ruiz-Pino, race Metal Pollution n the Mediterranean ea, Oceanol. Acta, 13, 481-488, 1990a. Bethoux .P., B. Gentili, . Raunet nd D. Tailliez, Warming rend n the Western editerranean eep Water, Nature, 47, 660-662, 990b. Boyle .A., S.D. Chapnick, . T. Shen nd M.P. Bacon, emporal Variability f Lead n he Western orth tlantic, . Geophys. e& 1, 8573-8593, 1986. Copin-Mont6gut ., Ph. Courau nd . Nicolas, istribution nd ransfer of Trace Elements n the Western editerranean, ar. Chem., & 189- 195, 1986. Dulac ., P. Buat-M6nard, . Arnold nd U. Ezat, Atmospheric nput f Trace etal• o he Western editerranean ea, , Factors ontrolling the variability f atmospheric oncentrations, . Geophys. es., 2, 8437-8453, 1987. Fowler S.W., P. Buat-M6nard, . Yokoyama, . Ballestra, . Holm and H.V. Nguyen, Rapid Removal of Chernobyl Fallout from Mediterranean urface Waters y biological ctivity, Nature, 29, 56. 58, 1987. Helmers, E., Untersuchungen ur horizontales erteilung usgewahlter SpurenmetaIle m Atlantischen cean. hesis 72 pp., University f Bremen, Bremen, 1991. Hopper . F., H. B. Ross, .T. Sturges, nd . A. Barrie, egional ource Discrimination f Atmospheric erosols n Europe sing he sotopic Composition f Lead, ellus, 3B, 45-60, 991. Lambert ., E. Nicolas, A. Veron, P. Buat-M6nard, . Klinkhammer, . Le Corre, . Morin, nthropogenic ead ycie n North-East tlantic Waters. Oceanol. Acta, 14, I,, 59-66, 1991 . Lambert C., A. V6ron, P. Buat-M6nard, M. Heyraud, F. Grousset nd W. Simpson, he Role of Large Biogenic articles n the Transport f Atmospheric b Down o North Atlantic ediments ceanol. cta, 4, 67-76, 1991b. Laumond ., G. Copin-Mont6gut, . Courau nd E. Nicolas, admium, Copper nd Lead n the Western editerranean ea, Mar. Chem., 5, 251-261, 1984. Mating H., D.M. Settle, .Buat-Menard, . Dulac and C. C. Patterson, Stable Lead Isotope Tracers of Air Mass Trajectories n the Mediterranean egion, ature, 30, 154- 56, 1987. Marmenteau . and A. Veglia, Determination f Seasonal ariations n the Atmosphertic oncentrations f Lead, Cadmium nd Polycyclic Aromatic Hydrocarbons n Monaco, Proc. of the WMO/UNEP Workshop Airborne ollution f the Mediterranean ea". Monaco, April 991, MAP Tech. ep. eries N. 64, 57-65, 992. Migon C., L. Alleman, . Leblond nd E. Nicolas, volution f the Atmospheric ead n Northwestern editerranean etween 986 nd 1992, Atriums. nviron., 14, 2161-2167. 1993. Pacyna . M., Estimation f the Atmospheric missions f Trace Elements rom Anthropogenic ources n Europe, mos. ttviron., 8, 41-50, 1984. Pattenden .J. and J. R. Branson, Relation between Lead n Air and n Petrol n two Urban Areas of Britain, Atmos. Environ., 1, I1, 2481- 2483, 1987. Remoudaki ., G. Bergametti nd P. Buat-M6nard, emporal ariability of Atmospheric ead oncentrations nd luxes ver he Nor[hwestem Mediterranean ea, . Geophys. es., 96, 1043-1055, 991. Ruiz-Pino D.P., C. Jeandel, .P. Bethoux nd J. F. Minster, Are the Trace Metal Cycles alanced n the Mediterranean ea, Palco. Glob. lanet. C mnge ec.), 82, 369-388, 1990. Ruiz-Pino .P., E. Nicolas, .P. Bethoux nd C. Lambert, inc Budget n the Mediterranean ea: A Hypothesis or Non-steady tate Behavior, Mar. Chern., 33, 145-169, 1991. Sherrell R.M., E.A. Boyle and B. Hamelin, sotopic quilibration between issolved nd Suspended articulate ead n the Atlantic Ocean: vidence rom 210Pb nd stable b sotopes, . Geop tys. es., 97, 11257-11268, 1992. Tatsumoto . and C.C. Patterson, oncentrations f common ead n some tlantic and Mediterranean aters nd n snow. Nature, 99, 350-352, 1963. UNEP United ations nvironment rogram). e plan bleu, veairs u Ba,•sin editerrangen., 42 pp., Economica ress, ads, 988. E.. Nicolas nd J.P. Bethoux, aboratoire e Physique t Chimie Marines, niversit6 ierre t Marie Curie, CNRS/INSU, P 8, 06230 Villefranche ur Mer, France. e-mail' bethoux @ccrv.obs-vlfr. r). D. Ruiz-Pino, aboratoire e Physique t Chimie arines, niversit6 Pierre et Made Curie, CNRS/INSU, Boite 134, tour 24-25, 4 place Jussieu, 5252 Paris edex 5, France. e-mail: miz@ccr.jussieu.fr). P. Buat-M6nard, 6partement e G6ologie t Oc6anographie, RA CNRS 197, Universit6 de Bordeaux , 33405 Talence Cedex, France. (Received ctober , 1993; evised pril , 1994; ccepted ay 0, 1994.)
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