Short-term impact of Vectron (OMS 3002) on the aquatic invertebrate fauna

,,, Ir ONCHOCER.CI.{SIS CONTROL PROGRAMME IN WEST AFRICA PROGRAMME DE LUTrE CONTRE L'ONCHOCERCOSE EN AFRTQLTE DE L'OUEST VECTOR CONTROL UNIT AQUATIC MONMORING DTVISION ocP/vcu /ss{le3.z SHoRT-TERM TMPACT OF VECTRON (OMS 3002) ON TI{E AQUATIC IIIVERTE,BRATE FATJNA A Impact on benthic insects Multiple gutter tests were carried out at Mango on the Oti (Togo), from 12 to 17 May 1993, in order to evaluate the toxicity of Vectron in comparison with that of permethrin, pyraclofos and OMS 3050. The physico-chemical factors measured during the tests have been recorded in the following table: The first test was of the classic type with a24-hr post-larviciding flrift collection with a view to evaluating the overall toxicity of the products. The second test concerned five increasing doses applied simultaneously in two parallel gutters for each insdcticide in order to study the impact of the products on the differeirt taxa present in the gutters. The pH, the temperature and the turbidity are comparable to the values generally observed during this period of the year on many watercourses in the Prograrnme area. They are not Iikely to affect the toxicity of the products tested although high temperatures cause a decrease in the toxicity of pyrethroids and an increase in that of organophosphorus compounds. 1. Overall comparative toxicity of the larvicides The mean detachment of the total fauna per insecticide teste<i and that of ttre principal taxa present in the gutters will be taken into account. At the operational doses, Vectron (OMS 3002) presents a drift comparable to that of pyraclofos, slightly less than that of OMS 3050 but far below that of permethrin (Fig.l). The main difference between Vectron and pyraclofos resides in the fact that Vectron is more active than pyrclofos within the first hour of the application of the product (66Vo of I Factors Date pH Conductivity (pslcm) Turbidity (JTU) Alcalinity (ppm) Phosphate(pp-) Nitrate(ppm) Temperature("c) 17H 13/s/e3 7.5 94.5 15 100 <1 < 1.1 34 14/s/e3 7.4 92.3 20 33.5 ts/s/e3 7.5 94 15 98 <L <L 34 I I2 the drift occurs within 30 minutes of the treatment as against 39%o for pyraclofos). Furthermore, generally speaking, Vectron is less selective as regards the Trichoptera and Ephemeroptera. On the other hand, pyraclofos is more active on the Simuliidae and Chironomidae as indicated in the table below: ' * "'r I tc Lt t"tf r,\\tt J C )o*" ' r"*.rr',rtiL"J t$.. C,t{ ,.,.'[.r 6r'; 1* /6\ U-|."r, ,| - \^n C. F\li (l !iiI I I{ ,O"VilI L+t.."( Cf"-,frJ /1ri (+ +l F,k,6 q.3 )t.5 h.t It is interesting to note that OMS 3050 is the least effective larvicide against the Simuliidae at the doses tested and that its toxicity on the non-target fauna is generally at least equivalent to that of Vectron. We wanted to know, subsequently, the level of change to be expected if these products were used in river. The index proposed by Elouard and Simier in 1990 and which showed a good correlation between the values observed in the field and those calculated (theoretical) from the gutter test data was used., The relationship that had been found by the authors from three insecticides (Abate, fu H-14 and Chlorphoxim) is: Y = 0.089x + 1.86withr = 1 By including pyraclofos, we obtained the following relationship: Y = 0.083x + 1.98withr = 0.99 Since this index was established on the basis of eight taxa (Baetidae, Caenidae, Tricorythidae, Hydropsychidae, Chironomirii, Tanytarsini, Tanypodinae and Orthocladiinae), we calculated the index for Vectron and OMS 3050 by using the detachments of the same ta:<a in gutter. The following values were obtained: $naclofos(0.1 mgl lxlOmin) oMS 3050 (0.025 mg/ lxlOmin) Permethrin (0.015 mel lxl0min) z t Vectron (0.03 mgl Ixl0min) Non-target fauna 47 43 56 9l Ephemeroptera 6t 54 66 97 90Trichoptera 24 15 51 90Simuliidae 56 9l 31 52Chironomini 3 45 10 80Tanypodinae L3 23 t7 Orthocladiinae 38 68 13 Chironomidae 15 69 7013 34 -i-. li 3Abate B.t Chlorphoxim Srraclofos Vectron oMS 3050 Permethrin %o Mortality Mean index 24 13 58 26 33 42 63 Observed 4 3 7 4.7 Calculated 4.7 5.5 7.5 The calculated value of the benthic conmunity change index for Vectron (a.7) is comparable to that observed for pyraclofos (a.7). It could therefore be expected that the changes which the userof Vectron would cause on the benthic communities would be of the same proportion as those brought about by pyraclofos. However, as was seen in 1990 on the White Bandama after 11 pyraclofos treatment cycles (Fig.Z), the community structure which was established is halfivay betwebn that due to B.t. H-14 and that due to carbosulfan and permethrin; chloqphoxim was not used on this watercourse. 2. (a) Toxicity of different doses on the macrobenthos Vectron In two paralfel gutters having comparable discharges, treatment was made every two hours with five increasing doses of Vectron (0.015, 0.03, 0.06, 0.15 and 0.3 mg/l x 10 min). The maximum number'of ta:ra collected after the Vectron treatment was24 for doses 0.15 mg/l x 10 min. and 0.3 mg/lx 10 min., as against 23 at 0.015 mg/lx L0 min., the difference being relatdd to the entry into the drift of a few Elmidae at the highest doses. It will be noted that all the taxa affected entered the drift within 30 minutes of the Vectron treatment and then the number decreased regularly (Fig. 3a). However, instead of the gradual increase iq the number of ta:ra after the dose increase described by Yasuno (1981) for temephos, a debrease was rather recorded at doses 0.03 and 0.06 mg/l x 10 min before a new increase ocCurred at 0.15 mg/l x 10 min., i.e., at five times the operational dose. All the tar,alsee-ed therefore to react at the lowest dose of Vectron. The individuals of some ta"xonomic groups (for example Chironomini) which did not drift during the first treatment entered the drift only aftei the treatment atl0'.t5 mg/l x 10 min. Could it be a difference in the susceptibility of the species which mdke up these. ta:ronomic groups or individuals having found conditions which allow them to be less exposed to the product's impact? , I ','l , 4For most of the families, the greatest detachments occurred at the dose of 0.03 mg/l x 10 min. (0.06 l/m3 s-r) as shown in Fig.4. An increase in the dose does not necessarily cause a higher detachment. For the Chironomidae which are known not to be very susceptible to the effect of pesticides, the highest detachment values were recorded at the dose of 0.03 mg/l x 10 min. The same applies to the Caenidae. As regards the Philopotamidae, though they are relatively susceptible to organophosphorus compounds, the same observation was made. An analysis of the toxicity of Vectron on the principal species of Hydropsychidae shows that the rcs,, are very close to the operational dose of 0.06 l/m3 s-1. On the other hand, the I-C, is almost 50 times higher for Cheumatopsyche falcifera, C. digitata, and C.copiosa. It is more than 200 times the operational dose for Amphipsyche senegalensis. For Neurocaenis spp (Tricorythidae), the LC, is comparable to that of the Hydropsychidae but the I-Cse is thre6 times less (Table 1). Vectron $naclofos oMS 3050 Permethrin LC, 0.02 Lr.,, rcso rc4 lcso Lr, rcso l.c, C. falcifera r.23 1.3 174.4 0.004 0.012 0.13 C. copiosa 0.03 1..4 1.5 117.4 0.009 t.6 0.0t2 0.16 C. digitata 0.05 1,.87 4.9 553.7 0.003 0.54 0.023 0.12 A. senegalensis 0.03 8.6 0.49 6.7 0.07 7.2 0.006 2.M Neurocaenis 0.03 0.49 0.47 1.37 0.028 0.87 0.0004 0.12 P. bertrandi 0.003 1.7 0.03 272t.9 0.002 33.7 0.0005 0.26 ble L I-ethal doses ( ta-na under the 1c1''1[ ".] t [* b) hnaclofos in mg/l x 10 min.) for 50 and 99Vo mortality of some r i effect of antiblackflv larvici des/ r",s'(' '-(.dlra( -l', *'" (t ' i ,,t r t ,t-*..^<l^xY.d t ^'tL" GL. nri.. r ,-''"'lrts ' Increasing doses of pyraclofos (0.05, 0.1,0.2,0.5 and I mg/l x 10 min) were applied in two parallel gutters at an interval. o.f nvo hours. The drifts were collected every 30 minutes and the results expressed in number of ta:ra affected and in percentage of detachment for each of the taxa studied. The number of taxa collected in the drift was maximal (23 tw<a) at 0.1 mg/l x 10 min (Fig. 3b), therefore at the operational dose, and at t mg/l x 10 min., i.e., 10 times more. At doses 0.2 and 0.5 mg/l x 10 min., the maximum number of ta:<a present in the drift was 20. In considering the principal families present in the gutters treated, it could be noted that the Simuliidae and Baetidae had a considerable detachment rightfrom the treatment ,,,f l I J { 5at half the operational dose (Fig.s). Despite the dose increases, the detachment percentage was low at 0.1 and 0.2 mg/l x 10 min. before increasing at 0.5 and 1 mg/l x 10 min. As regards the Hydropsychidae and Philopotamidae (Trichoptera), the dose increases led to drift increases up to 0.2 mg/l L0 min. (nvice the operational dose) at which the detachment was ma:rimal. For the Chironomidae (Diptera), the ma:rimum drift was recorded at the operational dose while for the Caenidae and Tricorythidae the greatest drifts corresponded to the highest doses. All the benthic invertebrate families did not reacl in the same way to pyraclofos. While the Simuliidae and Baetidae became detached at the dose of 0.05 mg/l x 10 min., the Tricorythidae and Caenidae were affected mainly from 0.5 mg/l x 10 min. onwards, i.e., a susceptibility that is 10 times less. This greater susceptibility of the Baetidae is confirmed by the rcs.s of Pseudopannota bertrandi and Centroptilum + Baetidae compared to the LCro of Neurocaenis sp (Table 1). A comparison of the LCro. and LC* calculated for the principal species identified (Table 1) shows that Vectron is more toxic than pyraclofos. c) Permethrin I The number of taxa present in the drift was ma.nimal (22 taxa) right from the dose of 0.0075 mg/l x 10 min., i.e., half the operational dose, as was the case with Vectron (Fig. 3c). The treatments made at doses 0.015, 0.03, 0.075 and 0.15 mg/l x 10 min. did not lead to an increase in the number of ta,xa in the drift. : The Simuliidae Caenidae and Tricorythidae experienced their greatest drift at half the operational dose. The fauna that remained in the gutter was not affected more by the higher doses. As regards the Chironomidae, permethrin caused the greatest detachment at the dose of 0.075 mg/l x 10 min. (five times the ioperational dose) while for the Philopotamidae 0.03 was the most harmful dose '(Fig.6). With regard to the Hydropsychidae, the greatest drift was at 0.015 mg/lx 10 min. (operational dose). However, the LCro. and LC* calculated for the identified species show that Neurocaenis sp. is more susceptible than Hydropsychidae to permethrin. It will be noted that although Neurocaenis sp and Pseudopannota bertrandi have LCrou 100 times less than those of the Hydropsychinae (C. falcifera, C. digitata and C. copiosa), the I-Crr" are comaprable or even slightly higher. It seems. therefore. that the susceptibility at low doses does not mean easier destruction,of the populations at higher dose. In fact, if 50Vo mortality of Neurocaenis sp. and P. bertrandi is recorded at a dose 30 times less than the operational dose, the doses required to obtain 99Vo mortality of Neurocaenis and P. bertrandi are 10 to 20 times higher than the operational dose. In other words, 300 to 600 times the dose that causes 507o mortality is required to obtain 99Vo mortality of these organismi. 3. Conclusion Although Vectron is a pseudopyrethroid, its impact at the operational dose on the benthic insects taken as a whole is quite comparable to that of pyraclofos and far below that of permethrin. u l< N ) 6Almost all the ta(a present in the gutters experienced an impact of Vectron like permethrin at half the operational doses with the result that an increase in the number of ta:ra in the drift was witnessed with the increases in the insecticide doses in the systems, contrary to what had been reported by some authors for temephos. As regards the toxicity of the products on the ta:ra for which the rcs.s and I-Qr. were calculated, it was noted that the rcs., of Vectron for the Cheumatopsyche were twice those of permethrin on the same ta:ra. On the other hand, Vectron's LCer. were 10 times those of permethrin. OMS 3050 presented the lowest rc* while pyraclofos was the least toxic of all. B. Impact on shrimps 1. l-aboratorv tests on Caridina africana The tests were carried out by IDESSA/Bouake under a contract signed with OCP. The data were the subject of a report presented by tl : Institute. For an exposure time of two hours, the mortalities recorded in tanks made possible the calculation of the following lethal doses. i LCro - 2hrs: 0.015 mg/l < = > 0.18 llr1e/l x 10 min. LCr, - 2hrs: 0.073 mg/l < = > 0.88 mg/l x 10 min. It can be noted that six times the operational dose, which is 0.03 mg/l x 1.0 min., is needed to cause 50Vo mortality of the Caridina and 30 times this same dose for 95%o mortality. It should be pointid out that the LC, - 2 hrs for permethrin is 0.036 mg/l x 10 min. (nrice the operational dose) and the I-Ces - 2 hrs 0.1 mg/l x 10 min. (seven times the ope;ational dose). 2. River tests on Caridina africana Two tests were conducted at different discharges (1a7) m3/s. and 19 m3/s.) on the I-eraba. The physico-chemibal factors measured during these testts are presented in the table below: t ;0 "{ ,| Discharge(.'/s) pH Turbidity(.rru) Conductivity(pslcm) Temperature(08h00) Alcalinity(ppm Ca cor) e/e/e3 t47 6.4 40 3t.7 25 "C 68 22/70/e3 t9 6.7 25 42 ?g "c il 7 I During these tests observations were made on the drift of the Caridina in the treated section as well as in the untreated section just upstream. The current velocuty within the nets and the distance between the insecticide application point and the location of the nets in the treated area are given in the following table: Current velocity (m/s) Distance from treatment (m) Time of treatmentTest net Control net e/e/tee3 0.52 0.37 244 12h00 22/10/1ee3 0.58 0.61 200 r2h30 ; The drift nets were sampled every four hotirs for 48 hours centred on the spraying. The individuals collected just after the treatment were kept under observation in cages placed in the untreated section in order to monitor their fate in uncontaminated water. (a) Test conducted on 9/9/93 The drift nets were placed or 8/9/93 at 12h00 and sampled every four hours up to 12h00 on 70/9/93, i.e., 24 hours after the treatment. The number of Caridina collected during the different net samplings is recorded in the following table: In the rainy seasor\ the approaches to the watercourses are often non-existent, which does not facilitate the finding- of sections comparable from all viewpoinis. The data recorded show here that the sections are different since the control net did more catching than the test net. It has therefore been decided, in'this'analysis, ,to.consider the test net 8/e/e3 e/e/e3 t0/e/e3 16h 20h 24b 4h 8h Lzh 16h 20h 24h 4h 8h tzh 'Control net 0 2 4 2 1 0 0 1 2 2 0 1 Test net 0 0 1 0 5 0 1 1 0 0 4 0 period from 12h00 on8/9 to 12h00 on9/9 as the control and compare it with the followingperiod. . ' { 8It witl then be noted that the total number of Caridina collected is the same for the nvo periods (pre- and post-larviciding). Considering the number of individuals caught per sampling, it is noted that there have been no modifications also which could be attributed to the effect of Vectron (Fig.7). AII the individuals caught after the treatment were alive at 12h00 on l0/9. (b) Test conducted on 22/10/93 The drift nets were placed at 12h00 on2L/9/93 and the samples taken every four hours up to 12h00 on?3/9/93, i.e., 24 hours after the treatment. The individuals collected after the sprayrng made at 12h30 ot22 October were placed under observation in cages put in the untreated control section. The following table shows the Caridina catches in the trvo zones during the whole study period. Control net The decrease in water level improved the presence of Caridina on the lrraba, as shown by the drift net catches. During this test, the nets were placed in the same sections as in September 7993. The evaluation of the drift of the Caridina over time is quite comparable in the nvo zones (treated and control) for the two periods (p.e - and post-larviciding with Vectron). The maximum drift was recorded at night, between 20h00 and 24h00, while the minimum occurred between 12h00 and 16h00 (Fig.8A and B). It was only after thp treatment (at 16h00) that a difference was observed benveen the drift in the two zones. I Furthermore, if the changes which occurred in the drift of the Caridina,in one zone during the second series of 24 hours are evaluated and compared for the two zones (Fig.6) a divergence will be noted, at 16h00. For the rest of the time, the changes that occurred in the post-larviciding drift are comparable for the t'wo zones. There is therefore a short-lasting impact of Vectron on the young Caridina at a discharge of 19 m3/s. The contrary would have been surprising, takinq ipto account the susceptibility of these organisms and the size of the individuals collected in the drift ( < Icm). r It should be noted that none of the 29 individuals collected just after the larviciding (at 16h00 and 20h00) was dead24 hours after the treatment, which makes it to be said that at 19 m3/s. on the Lcrab4 Vectron did not cause any direct mortality of the Caridina africana. t 2t/t0le3 22/10/e3 23/10/e3 16h 20h 24h 4h 8h 12h 16h 20h 24h 4h 8h tzh 0 5 48 29 28 0 0 37 84 22 2 I Test net 2 2 17 10 10 0 t4 15 31 22 4 0 I 9C. CONCLUSION The tests conducted in gutter on the macrozoobenthos and in river on Caridina africana have enabled it to be noted that Vectron is an insecticide that is, relatively, not very toxic on the non-target fauna. Its toxicity on the total fauna is comparable to that of pyraclofos (47Vo detachment as against 42Vo for pyraclofos). The Chironomidae are less affected by Vectron than pyraclofos, OMS 3050 and permethrin at the operational doses. However, the Ephemeroptera are more affected by Vectron than pyraclofos, while the two products have quite a comparable toxicity on the Trichoptera. The change that the use of Vectron could cause on the benthic communities (calculated according to the index proposed by Elouard and Simier (1990) should be of the same level as that due to pyraclofos. As regards the Caridina, no direct mortality was observed even at 19 it3 /sec. on the lrraba. The few individuals encountered in the drift just after the treatment were all live juveniles (6-7 mm long) and remained so in the uncontaminated water 24 hours after the larviciding. ql fr l] rll G o J^)OJooo ?6 of survival AC,l O)ooo + J\r@(DOo()oo y- i--'t. I -+ I i T I + If I I i I T I If I I i I i I I -L I I I + I I I -1- I I + I I I + i I a I I I I I + o a o =.3o0 'El aO:i o= =.o =ooc o-6O-q$OIo6 o=' ='S. rtl f= l.Q =i.oQo sltio8ao+vo ooJ(D ra{* .{=(D O-(*) =o G 5' o$ o 0: o- o og o i lI i t i I a t I I O I a I I I ? I) ! I 1 3h00 13h30 14h 1 4h30 15h lbn 17h 18h * I It l I F I + I ) + i * I I ft If I I I * l ! * ,lt I +*ltl !/rt .l* +iiliilt? ? 'ii/i+ iltllrlllr+ ?iltJ tIrlt! l++ .iiiii,a*.rJlijJ* iilitiiIs? ltt 'I + *. 1 I o oc o Ta ? I) 8h30 19h th30 20h 21h 2?h ,) l/ s 1 a I I ? It,,t, ? Ia' 2h 6h 7h th 10h 13h * I I * i Ig I ,&4. I I * tt I I I{ I I i a J l) I I a I lt i t : > ti o JI\JCOS(JIOT\t@(.c,Joooooooooo o liiiii5*l;lltl'rlrrlrg'E 6 3 EdjqII, s3 8q =oo ='oo lr cHl I TAT TAP CAE u a o o 0 o CL D D tr D EI PSY o E tr o B' Bt oflcr corborulton t-t Bt ottcr pyroclotor I Bt oficr pcrm.rhrln A tndustrtol pollulion Foctoriol correspondence onolysls oPplied to the do?o for lhe treoted pcriod (Dcccmbcr 1985 to Morch l99O) ot Bemo uPslreom on lhc white Bondomo. Fig.2 l){ La, Figure )d: Trend ol lhe number of taxa colleeted in the drift atter treatment ol two parallel gutters with increased dosee of Vedron (Mango. Mq133) O0lfrngil'1Omn 0,03m9/'10mn 0,06mgi'10mn 0.I5mg/.1Omn 00.03 t]- )E 2E 15 10 T I I + I 'J I + I l J l I + I + { i i al ri l. T I i + I 25 28 5 \\! \\\ I I tri. L U \\ o lt,x 6t dz I .I b'ct\! '.. i -acr' tr 5 .l r,1 \ \ \\ra 10 r\ \l 0 5 0 O-c,OEg) (o ({) sr -C.F.CFGl (e O=OE$) (r) (\JErEOF O=O=o, cD c, c> @c) ! fi\ u t\.\B ilb.t\ l\ (OtJ)(o 9,C Fgure ){.Trend sver time ol the number ol tam colleded in tre drift dter trealment of the tro parallelgutters with increased doses of pyradofos (Mango May 93) 0.05mg/'10mn 0.1m-ql"IOmn B.2mg/-1Cmn ..Emg/,10mn a. mnn T rl T I t I I 1 i 1 i l I i I 25 l l I20i I I E ls t(!t ilzt0i I I 25 20 15 10 5 5 0 25 N r5 10 a o.-1 a \- i traxIj z FI lr 0 J ?,b Figure lr: Trend of number of tar<a collected in drffi after treatdrenl in a gutter with increasing doses of perm6thrin (Mango. Mai 93) 00075mg/.10mn 0 015mgil.10mn 0.03mg,.{.10mn 0,075 ' OO.lg 5 u f-6lo 10oEo-c) tY) (i) sr .c .c,N(', oco-c(tt F d) (rJ OF c) -c o Ec)q|(r)oE3@o) r H a r-...{ I a I t l t I 6€868€EEAI ''I 8 E* I fiEZ158 f'I6EEQ(') L--. a- --l Iime (hourtl EE t"{ n be Figure/: Toxicity of Vectron on the principale benthic invertebrate families tested in multiple gutters at Mango/Oti in Mai 1993 Baelde !06mol-lt]mn ClShCrlomn 03mq/ll(,mn Caantdd 0 0lSmgrFlomn 0 03m9/l'loma 0 05m9il'lOmn 0 t 5m9n-t onn 03mgf1omr .5 { 15 j ? r5 I 05 0 50 {5 t0 i5 30 25 l0 t5 10 5 -20 ! ,oItroIrs {0 i --lt: E;;{;;lrol5 U 1( l0 20 15 r0 5 0 ,c 50ta itrE--t.o !ao820 * 10 0 jn :5 !zo t,.tI :r, , 5 c 0l smgll-lomn 0 0l0 I t ,l I 1 i L -10 ln rt It l( 1G t 1 0 o c E I I x T o 8888&tat EEE!tEESt6ltCIETE6=-tIIrE SEtE.4tr'tE88aAdrt88tt8&,laatEtS6::& IEETlletiill8II8AEBEtittBEIE!!!E EEEEEEBEEEEE t888ataa Tmpr (hard) Tncorytrciae Trpt (lsrr6) rarrrcnonidoe E T 1 I I l5 3( 20 t5 t! I 0EEEBrtI;Gt BEBECTE' rtrt Hydropsycfidae .{l l5 30 25 2l ;; : 0 I 1 t I + j l o EEEEoooo E:38EEAEOFtsOEEEEEEEEEEEE9==gEEEEaaoo E 8 e.el'tGF -a- Srm ulrd ae \ E I ? s re 0 E .{ 2 R E{ 0 20 rs r0 0 I EEAE =cltt B - I ar ] J I '... :t ll .I 1 1 1 I a {4L Figurerd: Toxicity of pyraclofos on the principal benthic invertebrate families tested in multiple gutters at Mango/Oti in May 1993 Cacridrc Beolidec O O5rnor'1O 0.1 0,2 0.5 5 I 0.2 l0 s o E a 15 10 5 0 $ e) 6 a 15 10 5 0 0.50.10.6rngI'IOrn tl6 r $ x) ia tzo trsa ;10 5 0 :l ;r' c 1"',E-- i -'1.f ,.c *. .I :., t , r., 10 c 50 15 {0 s o a a l5 l0 5 0 'r 't t 1 I + .l fl T I 1 l J 'l 1 + o.f D fr \ I \ I h \ \ Iq o a't u 3GC3U)0Fo868€ Nat 8:86G3o I co IEo sssEhOFG858€ -, E-N(i) 8f86 o- -8lF I5 a6) e,trt5it) 60 ::,-' J,r );' IL, +30 h.- ; lj i l I 1 1 + I ; I I I 'l I ! I ,1 4 2 fJ to 1 t I t I b o I 4 i $ ,I \ tIa. E a E a 6 o xD * ! 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E=8fr 6- 6 a F - -8586 € 6- t6t+ fiBc 6 a8Jfi-8fB66-f--8686 6-F- FH+cIia It. /\,lit\ ilJ1 :\ \ 1 I I I I 1 i E 5f xg , -8686f, f - 8=866':' 8f8ff-f- 66f,5 SinIi.L ! \. 8f6- 8f 6 a .{ ii,,]'ii' ;III( ..212! .t=!f F' a 't .I I I 'f i I I I I 1{ Figure 7 : Comparrson of the drift of Caridrna before and after Vectron treatment rn the control zone and the treated one on the Leraba 1 (A) ControlZone 10 +BfT -----a--AfT + oz g' o -----fl ooooooo o o o o ioEEEECCtDossr@G/F(\TNOOF Time (hours) (B) TreatedZone, ,t: 1o I-:-:::--::--:-:::-:::-:::-:--^---------'. a + C,z CN o r- BfT ------+l- AfTI \, '\ o(> EN oo 6ct 1 I l oooooo L*&ossNNO Trme (hours) oo !(o t 4 -------r'--- r-H-| I1 trend of drift of Caridina in the trryo zones before (A) and after (B) treatmentwith Vearon atFi9 Comparative on the L6raba lrom 21 to 23f10193 0 + oz El -9 100 100 r (A) : Before treatment oooooo osrs(\rNo Time (hours) (B) . Aftertreatment ooqc ss(\to Time (hours) -r-- Conlrol -----{- Test ------{- Control ---nl- Test 1 ood oo COo oo(\ 0dz o -9 1 oq(o f oo ccj oq N oq o m \l r, ; .F a ,/ : -:'.::'.--:'_'- -: -7 - l1 Figure I : Comparative change in the drifl of the Caridina tn the two zones after the Vectron treatment on the L6raba in October 93 16.00 20.00 24.00 04.00 08.@ 12.00 t 700 600 500 400 300 ?00 100 cj- 700 -----{_- Test -------r- Temoin i iT I ii I i t I I I I i If I i + i it I -t I i I 600 + i 500 + i o 400+Cnl c, -E aoo +oi rolit\ 2oo + I rl 100 + I I0+ i -100 -L 0 001 1, {s2( a -A'