Adamson, J.K.

Beresford, N.A.

Howson, Gillian

English

NERC Open Research Archive

1I 3INSTITUTE DF TERRESTRIAL ECOLOGY(NATURAL ENVIRONMENT RESEARCH COUNCIL.)ITE Project 1113Final Heport AAFF/NERC CONTRACT•A COMPARISON OF 1986 AND 1987 CAESIUM ACTIVITIESOF VEGETATION IN THERESTRICTEDAREA OF NORTH WALES••••N A BERESFORD, GILLIAN HOWSON AND j K ADAMSONInstitute of Terrestrial EcologyMerlewood Research Station• Grange-over-SandsCumbria LA11 ojU August 1987This Report is an official document preparedunder contract between the Ministry ofAgriculture, Fisheries and Food and the NaturalEnvironment Research Council. It should not bequoted without the permission of both theinstitute of Terrestrial Ecology, and theMinistry of Agriculture, Fisheries and Food.•••CONTENTSPage1 SUMVARY 12 INTRODUCTION 23 MATERIALS AND ETHODS 3RESULTS AND DISCUSSION• 45 ACKNOWLEDCIENTS 56 R.EFERENCES 6••11 SUMMARYVegetation from sites within and around the restricted area of North Wales,visited initially in June 1986, has been resampled and analysed for 137Csactivity. At most sites the 137Cs activity has declined to less than 50%of the 1986 value. However, there are areas where the caesium activityremains high enough to warrant the continuation of restrictions on themovement and slaughter of sheep.2 INTRODUCTIONA nationwide survey of the 137Cs activity of vegetation resulting fromdeposition of fallout from the Chernobyl accident was conducted by the ITEin late May 1986. Particularly intensive sampling was conducted in NorthWales and Cumbria due to initial indications that higher deposition hadoccurred in those regions. In West Cumbria, North Wales and areas ofScotland, the caesium activity of vegetation was sufficiently high to causetissue levels in sheep grazing these areas to exceed the limit of 1000 Bqkg-1 wet weight, recommended by the Group of Experts established underarticle 31 of the Euratom Treaty meeting in Luxembourg. Consequently itwas necessary to place restrictions on the slaughter and movement of sheepfrom these areas.Although the caesium activity of vegetation declined rapidly in most areas,in large upland areas of West Cumbria and North Wales it remainedcomparatively high. It became evident that caesium uptake by vegetationwas occurring and that the need for restrictions in 1987 would be dependenton the caesium activity in the grazed vegetation of the new growing season.•The 137Cs activity of vegetation, collected in June 1987 from 26 samplesites, in and around the restricted area of North Wales, has been measuredto provide a comparison with activities of vegetation taken from the samesites in June 1986. The results may help to determine the potential forchanges in the size of the restricted area in 1987. A similar report(Beresford et al. 1987) compares the 1986 and 1987 137Cs activities ofvegetation from the restricted region of West Cumbria.00•3 MATERIALS AND METHODSTwenty-six sites within and around the currently restricted area of NorthWales, originally sampled in June 1986, were revisited in early June 1987.The location of sample sites is shown in Figure 1.Vegetation was clipped from 1 m2 quadrats to a height of 1 cm above groundlevel. Areas dominated by dead vegetation or species other than grasseswere avoided. The samples were dried at 80° C, weighed, ground and countedin plastic containers (130 ml) on a NaI(Tl) detector to determine 137Csactivity. The a most active samples were recounted on a high resolutiongermanium detector.Soil samples (20 x 20 x 4 cm) were taken from all sites. Soils wereallocated to a series of textural categories on the basis of the estimatedcontent of clay, silt, sand and organic matter. Soils dominated bymaterial from one category were simply given one category name (eg silt).Soils given 2 names (eg sand/silt) had significant quantities of materialfrom 2 categories, the first category being present in greatest quantity(sand in this examples). "Loam" was used for soils with significantquantities of material from 3 or more categories (eg sand, clay and organicmatter). The categories were:-1. Clay: particles of less than 2 pm diameter;2. Silt: particles of 2-40 um diameter;Sand: particles of 50 um - 2 mm diameter;Loam: mixed - see above;5. Organic: - humified plant material.Soil pH was determined using an antimony electrode pH meter.••RESULTS AND DISCUSSIONTable 1 compares the 137Cs activity of vegetation collected in 1987 to thattaken in 1986, and provides data on soil pH and texture. In 1986 23 of the26 samples were greater than 2000 Bq kg-1 dry weight, the maximum beins6410. In the 1987 resampling only one sample was greater than 2000 Bq kg-1dry weight and a further 6 above 1000 Bq kg-1. One sample however, had agreater 137Cs activity in 1987, than that of the sample taken from the samesite in 1986. Fourteen samples collected in 1987 were below 300 Bq kg-1,the detectors limit of detection. As in West Cumbria (Beresford et al.1987) the majority of samples greater than 300 Bq kg-1 dry weight in 1987were from low pH, organic soils.The data-from North Wales suggests a slower decline in activity than wasfound in West Cumbria. Most of the 1987 samples from West Cumbria whichwere above the limit of detection (ie > 300 Bq kg-1 dry weight), haddeclined to less than 30% of their 1986 activity. In contrast, 6 of the 12North Wales samples which were above the detection limit in 1987, had a137Cs activity greater than 30% of that of the sample taken from the samesite in 1986. However, the original detailed sampling of West Cumbria wasconducted 6 to 7 weeks before that in North Wales, consequently 1986 137Csactivities in Wales were generally lower than those in Cumbria.The 134Cs activity and 134Cs:137Cs ratio (approximately 1:2.72) of the 8most active samples are shown in Table 2.Assuming that the transfer coefficient (caesium activity of muscle Bq kg-1fresh weight/daily intake of caesium) for both 134Cs and 137Cs to lambmuscle is 0.79 (Howard et al. 1987), restrictions will need to remain inforce in those areas where the 137Cs activity of vegetation exceeds 1500 Bqkg-1 dry weight. As only 3 of the samples presented in the report aregreater than 1500 Bq kg-1 dry weight, the results suggest that the size ofthe restricted area could be decreased. However, since early July datafrom the live monitoring of sheep by the MAFF have resulted in therestricted area being increased. This apparent discrepancy may be due tothe timing of the vegetation resurvey; it may have been conducted too earlyin the growing season to show the full extent of caesium uptake by plantsthis year.It should be noted that the samples presented in this report were taken atpreviously sampled, specific locations one year after the original surveyto enable a comparison of current levels in vegetation with those ofvegetation shortly after the deposition. The results should not be used topredict seasonal variations of the 137Cs activity of vegetation over thecoming year.5 ACKNOWLEDGEMENTSWe would like to thankElizabethKing, Dr A D Horrill and Brenda Howard fortheir help during this study.•••••••6 REFERENCESBERESFORD, N.A., ADAMSON, J.K. & HOWARD, B.J. 1987. A comoarison of 1986and 1987 caesium activities in West Cumbria. NERC/MAFF ContractReport.HOWARD, B.J., BERESFORD, N.A., BURROW, L., SHAW, P.V. & CURTIS, E.J.C.1987. A comparison of caesium activity in sheep remaining on uplandareas contaminated by Chernobyl fallout with those removed to lessactive Lowland pasture. J. Soc. Radiol. Prot., 7.••••••137CsActivityofVegetationGrid19861987ReferenceBqkg-1ligkg-1drywtdrywt•0Table1SampleDecreasein137CsSoilSoilActivity(1986-1987)ClassificationpHBqkg-1drywt1282352850<300>550Clay6.422943472710<300>2410Cl.ay/Silt6.132843493170<300>2870Clay/Silt6.442933482860<300>2560Clay/Silt5.65312322320<300>20Clay/Silt6.262753683240<300>2940Clay/Silt5.87275361262013401280Clay/Silt4.3829732211501960+810Silt/Clay4.592853483390<300>3090Silt/Clay6.2102913472140<300>1840Silt/Clay6.6112933452330<300>2030Silt/Clay5.7122743692800<300>2500Silt/Clay4.7132763642680<300>2380Silt/Clay5.6142713515580<300>5280Silt/Clay5.6152763582020<300>1720Silt/Clay5.21627137420504201630Silt/Cl.ay4.31727536636004603140Silt5.0182903452080<300>1780Organic4.31927634064106405770Organic3.62027734420907801310Organic3.621272358327010502220Organic4.222266360521012903920Organic4.023271366301016101400Organic3.62426935941709603210Organic6.425268360499022502740Organic4.326274367404010103030Organic3.4Tabie 2Sample CaesiumActivityof Vegetation134cs 137Cs 134Cs:137Cs7 540 1330 1:2.4617 700 1890 1:2.6121 410 1070 1:2.6122 480 1360 1:2.8323 530 1490 1:2.8124 290 820 1:2.8325 900 2460 1:2.7326 360 1010 1:2.812600001623211428000012,62° 171371539.2019300000 3200003800003 6 00 0 0- H-Colwyn 3ayI 0 218 H•Balaa 5\ -7—380000•Bangor2225360000 — 2t•SnowdonPort madoc•340000320000 —-- 340000-- 3200001260000 280000 300000 320000Figure 1. Locationof sample sites•

A comparison of 1986 and 1987 caesium activities of vegetation in the restricted area of North Wales. Final report

http://nora.nerc.ac.uk/501174/1/ITE%201113%20%20O146938CR.pdf

A comparison of 1986 and 1987 caesium activities of vegetation in the restricted area of North Wales. Final report

Abstract

Similar works

Full text

Available Versions

NERC Open Research Archive