The Science of the Total Environment, 75 (1988) 11-20 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
METAL CONTAMINATION AT SHIPHAM
HILARY MORGAN Department of Child Health, Charing Cross and Westminster Medical School, Vincent Square, London SWlP 2NS (United Kingdom) 2.1 GEOLOGY
Shipham is located to the north-west of the Mendips on the Blackdown pericline approximately 600 foot above sea level. The village itself is underlain with mineralised dolomitic conglomerate, and bounded by hills of limestone to the north and Old Red Sandstone to the south (Fig. 2.1). To the west, some 10 miles away, lies the Bristol Channel. The Mendip hills consist of Mesozoic rocks which lie unconformably on the folded Palaeozoic strata. The intervening Carboniferous rocks have been entirely eroded at Shipham and the dolomitic conglomerate lies directly over the Old Red Sandstone. Earth movements which occurred in this area during Armorican times, folded the Carboniferous rocks into a basic periclinal form still evident today (Green and 343
Fig. 2.1. The mineralisation and geology of the village of Shipham (after Geological Survey of Great Britain: England and Wales, 1952).
((~ 1988 Elsevier Science Publishers B.V.
12 VVelch, 1965). A long period of denudation resulted in the formation of the dolomitic conglomerate during the Triassic period. This deposit is up to 100 m thick and comprises large and small boulders of Carboniferous limestone, sometimes dolomitized or haematized in a matrix of sand, gravel or marl. 2.2 MINERALIZATION Intense zinc mineralisation took place in the dolomitic conglomerate at the core of the Blackdown pericline (around Shipham). The mineralisation is thought to reflect the deposition of sulphides, by hydrothermal fluids ascending from depth, mineralising favourable lithologies within the Carboniferous limestone and dolomitic conglomerate, until stopped from rising further by impervious cap rocks of Keuper Marl or Liassic Clay. The mineralising fluids are believed to be basin margin migration waters, emanating from a deep water basin to the south (Ford, 1976). Mineralisation occurred in early Jurassic times, but there is evidence that much reworking and alteration of the original materials has taken place, with the zinc originally deposited as a sulphide, being oxidised to the carbonate, although lead remains unchanged as galena (PbS). Where the Carboniferous limestone is overlain by dolomitic conglomerate, the veins, which mainly trend E-W, continue unbroken from one rock type to the other. Much of the mineralised dolomitic conglomerate has been eroded, leading to a widespread redistribution of the minerals in the Shipham area. Two main forms of smithsonite (calamine, ZnCO3) have been identified. One has a honeycomb structure and is possibly formed by 'in situ' oxidation of sphalerite (ZnS), the other results from the chemical solution and reprecipitation of the metal as surface coatings or concretionary deposits. Specimens of each mineral type are preserved in the Russell Collection at the British Natural History Museum, London. Cadmium occurs as a guest element in the zinc carbonate ore at a zinc:cadmium ratio of ~ 100:1. Extensive weathering of the ore, as appears to have occurred at Shipham, produces deposits which are a mixture of ZnCO3, PbS, Fe oxides and calcite (Goodman, 1979). Mineralogical studies have recently been carried out on soil from around the old mine workings (Mattigod et al., 1986). Smithsonite (ZnCO3), leadhillite (Pb4SO4[CO312OH2) and barite were clearly identified, with smithsonite forming 5.7% of the mineral fraction of the soil (leadhillite 0.8%, barite 0.4%). Trace amounts of cadmium, iron, calcium and silicon were associated with the smithsonite. No discrete cadmium minerals were identified despite the use of sensitive detection procedures. 2.3 MINING Zinc ore was first worked from Shipham in the mid 16th century. The main area of mineralisation lay to the north and to the south of the village and formed the Rowberrow and Shipham 'runs' (Fig. 2.1). The veins were often
Fig. 2.2. ~Gruffy ground' at Shipham showing the bell pits as they appeared in 1981.
small, varying in width from 2.5 to 15 cm, but occasionally reaching 30-90 cm. Most of the ore lay close to the surface and it was possible to extract it by hand by digging shallow shafts down to the vein and piling the waste rock round the circumference of the shaft, forming 'bell pits' (Fig. 2.2). Once a vein was discovered the ore would have been removed with as little waste as possible. Frequently, calamine was found within a metre of the surface. Few pits went deeper than 40 m. One of the earliest accounts of the mining in the vicinity of Shipham was the letter of 1684 by Giles Pooley (Pooley, 1693), written at the request of the President of the Royal Society. The basic principles described remained valid over the entire period of mining. (See following page, first column.) The ore, once mined, was then washed, crushed and calcined at or near the site of extraction. Pooley's account continues with a detailed description of the treatment of the ore. (See following page, second column.) Although four calamine ovens were recorded at Shipham (Gough, 1930) the locations of all but one are now unknown. The remaining chimney still stands behind Court House in the centre of Shipham. The fumes produced from these furnaces killed off many of the trees in the area (Collinson, 1791). It is likely that particulate fallout from this source was responsible for much of the metal dispersal, because the cadmium was vaporised to some extent during the calcining. Airborne contamination would also have arisen from dust produced by working and crushing the ore.
14 As to the finding out the Calamin¢, which I think tl~e fir~ thing to intbrm you of, the Groovers tell me there is no certainty at all, but that it is a meet Lottery : They are neither certain of it from tl, e Surface of the Earth, which, as they obf~rve, gives little or no figns thereof; fometimes they f.~yan oily Steam and Smell arif&h out of theEarth where they guef~ rome Mines to be, hut not Calamine; nor from the Nature of the Ground, it being foam fometimes in Meadows, fometimes in Art. ble, lbmetimes in Pafture ; and as I have obferved, molt commonly iv, barren and rocky Ground : Neither from the Colour or Tafie of the Waters running thereabouts, they being muci: of the f~me Colour, Tat/e, Clearnef~ and Wholfomnefs with other Water : Nor from the withering of the Gra(~, upon the Superficies of the Earth, or the Leaves of the Trees, they being as freCh where Calamine lies, as in any other place. But this I obferve, thatthey alwaysdig for it upon, or near t~e Hills; for they expe& none in thole Grounds which have no Communication with Hills. The Method tl2ey take for finding out a Vein is by digging a Trench as deep as till they come to the Rocks where they expe& it lies, acrofs the place where they hope for a Gour[~; which Trench they generally dig from North to South, or near upon that Point, the Cour.~s ufually lying from Eaf~ to "¢¢e1~, or at Six a Clock, as their Term is. Though this is not conf~an'. neither ; for fb,netimes the Couri~s, Seams or Rakes as they cail them, lie at Nine a Clock, and fomedmes are perpendicular, which they call the High time of t!:e P-~,y, or T~clve a Clock; and there Courffs they elteem the bell Thel~ Seams or Courfes run between the Rocks, _-eneraily wider than thole of' Lead-Ore, unlef~ they are inclol~d m very hard Cliffs, and then they are as ~arrow asthe Veins of Lead. The Colour of ~iic Eartii ',~!,~re Ca/ami~te lies, is generally a yellow Grit, hat f~.m~-timc~black; for all Countries, as they '.crm their u/~der-groui~dWorks, are not alike. Calamine it felt"is of f;~veralColours, [0me white, rome reddi~, lbme grey[[h, rome blackifb, which is counted the belt ; but when this is broken, it is of feveral Colours. In working tbr it below in the Countries, they ufe the fame way a,ad |nflruments as they do in Lead-Mines; and fometimes they light upon a good quantity of Lead, but always find lome Eyes of Lead among the Calamine, which in ordering of it they l~parate : Though I think in Lead Mines they do not always find Calamine. In landing of tile Calamine rome pieces are bigger than others of different fizes, as other Stones are, and mix~ with the gritty Earth ; yet I have been informed by a Per(on concerned in thele Works, that they have found one entire piece of 8 or , o Tun, which by reafon of its bignefs was forc'd to be broken in the Groove before it could be landed ; but generally in thefeGrooves where I made my Enquiry, it rifeth in [mall Particles, rome more, rome lefs, and (brae about the bignel~s of a Nut, and this they call a final[ Calamine. In ancient Works, (which are thot;" that have been forfaken and afterwards workt in again) Damps and Staunches form:times ari/~, but never in new Works ; but that there Damps art[e, an experienc'd Groover tells me is the Fault of thole Workmen, that do not take care to carry Air along with them, which is done by Air-Shafts, as in LeadMines.
When they have landed a good quantlt)' of tiffs C~/amine, which is clone by winding it up in Buckets ti'om their Works, they carry it away to the places where they waflh clean or bnddle it, as their Term is, which they pedbrm atter this manner. They enclot~: a lmall piece of Ground with Boards or Tuttis, through which a clear Stream of Water runs ; within this Enclofure they fllovel their Calamine with the rett of the impure affd earthy parts; and there impure and earthy parts tile running Water which comes in at one end of the Enclofure carries away at the other end, and leaves the Lead, and the Ca&mine, nod the other heavier flony and [parry parts behind ; and for the better cleaafing or buddling theCalamine while it is in this Enclofure, they often turn it, that (o the Water pafl,ng through may wafh it the better : When they have thus waffled [t with this running Stream as clean as they can, having rak'd up the bigger parts both of the Lead and the Calamine, they atterwards put the [mailer parts, that they may lore none of their Ore, into Sieves made of ftrong Wire at the bottom ; and thef~ Sieves, with the Calamine, Lead, and the Remainder of the earthy, liparry and fl.ony parts which the Water could not wafh away, they often dip and lhake up and down in a great Tub of Water, by which [baking of the Sieves, the parts of the Lead which is mixt amongtt the Calamine rink or pitch down to the bottom of the Sieves, as being hear[ell, the parts of the Calamine in the middle, and the other [parry, [tony and traflay parts rife up to the top, which as they rife, they skim off, and throw among the re/l of the Rubbith, and then they take nit the Calamine, and after that the Lead. When they have thuscleanfed the Calamine as well as they can, it being not yet clean enough, they are forc'd to fpread it upon a Board, and fb pick out with their hands the trath and ftones that remain. I cannot tell whether you will ~pprel~.end • this Defcription of their buddling the fmal~er Calamine; but you mu~ know that all of tt doth not require fo much trouble ; t o r rome rifeth big enough out ot the Works to be cleanfed and pickt fit tor the Calcining Oven without all this Charge and Pains: And 1 have ti:en (~:veralLoads of this great Calamine, whiclx had no mixture ot Earth or Traih in it. After the)" have prepared their Calamine by wafhing and picking, they then carry it to the Oven, which, at lear that which 1 law, is much bigger than any Bakers Oven, ar.d made much inthe fame Falhion, only this way of heating, burning or baking the Calamite is different ; tbr it is not done as bread is ~ lbr they c~.tt i,t their Coals into a Hearth made on one fide of :he Oven, which is divided from the Oven it fell by a Hem or Partition made open at the top, whereby the Flame of the Fire pa~th over, and tb heats and bakes the Calamine. They let it lie in the Oven for the [pace of Four or Five Hours. the Fire burning all the while, according to the !~rength of the Calamine, rome being much llroager than other, and fo requirivg longer time ; and while ,t continues in the Oven. they turn it Feveral timeswith i'ong Iron Cole.rakes ; when it is fufficiently burnt, baked and drieS, r!:~v Lent it to a Po~vder with long Iron Hammers !iRe M[::~e._':, upon a thick Plank, picking out ~hat Stone~ £:~:-~ find amongfi it ; fo that at lift the Calami~e is reduced to Duft: From the Oven it is convcyed m Sacks to tbme Port, where being bought by the McrchTnts, it is carried beyond-Sea, commonly 1 think to Ho/land, whether I refer you to be further informed concerni nff~the ufe of it.
Fig. 2.3. Soil map of the Shipham area (after Findlay, 1965). The mines were very active during the 18th century: in Shipham alone there were more than 100 of these mines at work, many of them "in the street, in the yards and some in the very houses." (Collinson, 1791). By 1795 there were between "400 and 500 miners employed and the whole region was given to the mines, and practically the whole livelihood of its inhabitants depended on them." (Billingsley, 1795). In 1797 Maton wrote that " a t particular hours of the day when their labours cease they may be seen crawling out of (their mines) exactly like rabbits from their burrows." The ore was transported to Bristol for use in the brass industry. Gradually, with the collapse of the English brass industry, mining declined and had ceased by the end of the 19th century when little ore remained unworked. Documentation on the closing stages of the mining at Shipham is scarce. It would appear t h a t by the middle of the 19th century mining was declining. Although as late as 1870 deeper shafts were sunk in the hope of discovering more ore, these do not appear to have been successful. 2.4 SOILS The soils in this area (Fig. 2.3) are derived from three main parent materials: Carboniferous limestone, dolomitic conglomerate, and Old Red Sandstone. In addition, Keuper Marl occurs near the village of Star (slightly to the northwest of Shipham), and is overlain in places by loamy head deposits. These materials give rise to brown earths or gleyed brown earths, depending on the
16 TABLE 2.1 Summary of the soils found in the Shipham area and their main characteristics (After Findlay, 1965; Findlay et al., 1984) Soil series (association)
Soil characteristics Surface Subsoil
Neutral to acid, Neutral, silty shallow stony, clay loam, silty loam, silty reddish brown clay loam. Brown red brown
Old Red Sandstone
V. acid to acid Moderately reddish brown acid, reddish loam, sandy loam brown loam
Tickenham (Whimple 1)
Sandy drift over Keuper Marl
Neutral to acid stony, brown to grey brown, sandy loam, loam
Neutral, reddish brown to weak red sandy clay
Worcester (Whimple 1)
Neutral to acid, red brown to grey brown, clay loam, silty clay loam
Neutral reddish brown or grey, faintly mottled silty clay or clay
Neutral to acid, stony red brown clay loam
Slightly acid to neutral, red brown clay loam
freedom of drainage. In the gleyed soils, the lower p a r t s of the profile are mottled, i n d i c a t i n g t h a t d r a i n a g e is impeded due to the c l a y e y m a t r i x of the soil p a r e n t material. The r e l a t i o n s h i p s w h i c h exist b e t w e e n the soil series, t h e i r d o m i n a n t c h a r a c t e r i s t i c s , a n d t h e i r p a r e n t m a t e r i a l s are given in Table 2.1. The soils in this a r e a (along with all t h o s e in E n g l a n d a n d Wales) h a v e r e c e n t l y been reclassified ( F i n d l a y et al., 1984) and the new soil a s s o c i a t i o n s are s h o w n in p a r e n t h e s e s in Table 2.2. 2.5 LAND USE After the m i n i n g ceased m u c h of the Cgruffy' g r o u n d was levelled and r e c l a i m e d to provide g r a z i n g for cattle and sheep. L a n d use in the r e g i o n is m a i n l y a g r i c u l t u r a l , with some w o o d l a n d p r e s e n t on the limestone hills to the north-west. P l a n t c o v e r on the p e r m a n e n t p a s t u r e is diverse and includes species c h a r a c t e r i s t i c of well d r a i n e d soils and r o u g h grassland. Elsewhere,
POPULATION 12001 1100~ 1000900800700800500 t 4007 3002001000
1791 18'01 18'11 18'21 18'31 18~4111=1'5118'61 1871 18`81 1891 1S()1 19'11 1921 19~1 19~¢11951 19`81 1971 19'81 YEAR
Fig. 2.4. Shipham population 1791-1981 (Officeof Population and Census Statistics). ryegrass (Lolium perenne) and clover (Trifolium repens) leys have been established to provide temporary grazing, and cut grass for silage or hay. Where grass has been sown on land which was previously mined, some problems have occurred, with plants becoming yellow (chlorotic) and then dying, leaving native 'weed' species to colonise the disturbed area. 2.6 DEVELOPMENT OF THE VILLAGE Throughout the 18th century Shipham flourished as a mining village, and the miners cottages gradually filled in the open space until the common was reduced to narrow lanes and alleys twisting around and between the randomly placed buildings. This gave Shipham a distinctive cellular street plan which it maintained until recently. Old street names, such as Hind Pits and Barn Pool, still remain as evidence of the mining heritage. Although records suggest t h a t mining was at its peak in the Shipham area in the mid 18th century, it has not been possible to trace the size of the population prior to 1791. At this time the population in the two villages of Shipham and Rowberrow was around 700 individuals. Numbers continued to rise until 1831, when they stabilised briefly before rapidly
Fig. 2.5. Aerial photograph of Shipham taken in 1948 (bell pits and mineralisation clearly evident to the north and south) (to same scale as Fig. 2.6). declining until, in 1911, t h e r e were only 437 people in the two parishes. The p o p u l a t i o n at R o w b e r r o w c o n t i n u e d to dwindle - j u s t before the s t a r t of the Second W o r l d W a r o n l y 56 people r e m a i n e d - and the parish was combined with S h i p h a m for census purposes (along with the tiny h a m l e t of Star). In S h i p h a m itself, however, n u m b e r s b e g a n to rise rapidly after the Second W o r l d War, reflecting an i n c r e a s e in mobility a m o n g s t the p o p u l a t i o n generally. Most of the 1092 individuals r e s i d e n t in the village at the time this s u r v e y was i n s t i g a t e d w o r k e d outside the area. In the 30 y e a r s from 1931 to 1981 the p o p u l a t i o n of S h i p h a m doubled (Fig. 2.4); this was the r e s u l t of new h o u s i n g d e v e l o p m e n t w h i c h has o c c u r r e d on p r e v i o u s l y mined land. An a e r i a l p h o t o g r a p h of S h i p h a m t a k e n in 1946 is shown in Fig. 2.5: the m i n e r a l i s e d a r e a and r e m a i n i n g bell pits are clearly visible. A c o m p a r a b l e map of h o u s i n g in S h i p h a m in 1981 (Fig. 2.6) shows t h a t infilling w i t h i n the village is complete, and the m a i n areas of d e v e l o p m e n t can be seen to the n o r t h and south.
19 , .
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"" "--~tt:" :
".s ...... L~
/ .... j,
i~ P A,
,'. ~::: ° --k!
Fig. 2.6. Street map of Shipham in 1981 showing the extent of recent housing development (shaded areas indicate property built in the last 25 years). 2.TCONCLUSIONS
Between 1650 and 1850 the village of Shipham was the centre of the British zinc mining industry. The zinc was present as zinc carbonate, and cadmium is commonly found as an impurity in this mineral. Once the mining ceased much of the previously mined land was levelled and used for housing and agriculture, although some old mine workings can still be seen. In 1978, about a thousand people resided in the village, but most were employed outside the area. REFERENCES Billingsley, J., 1795. General View of the Agriculture of the County of Somerset. 2nd edn., with additional notes 1798, Cruttwell, Bath. Collinson, J., 1791. History and Antiquities of the County of Somerset. 3 Vols, Cruttwell, Bath. Findlay, D.C., 1965. Soils of the Mendip District of Somerset. Memoirs of the Soil Survey. (Sheets 279 280). Rothampstead Experimental Station, Harpenden. Findlay, D.C., G.J.N. Colbourne, D.W. Cope, T.R. Howerd, D.V. Rogan and S.J. Staines, 1984. Soils and their use in south western England. Soil Survey of England and Wales, Harpenden.
20 Ford, T.D., 1976. The ores of the South Pennines and Mendip Hills, England: A comparative study. In: K.H. Wolf (Ed.), Handbook of Strata-Bound and Stratiform Ore Deposits. Vol 5, Regional Studies. Elsevier, Amsterdam, pp. 161 195. Geological Survey of Great Britain (England and Wales), 1952. Mapped on a Scale of 6 inches to 1 mile, Sheets ST 45 NW and ST 45 NE. Goodman, J.G., 1979. The Dispersion of Cadmium, Lead and Zinc in Agricultural Soils in the Vicinity of Old Zinc Mines at Shipham, Somerset. Unpublished M.Sc. Thesis, Imperial College, University of London. Gough, J.W., 1930. Mines of Mendip - revised 1967. David and Charles, Newton Abbot. Green, G.W. and F.B.A. Welch, 1965. The Geology of the Countryside arounds Wells and Cheddar. (Explanation of One-Inch Geological Sheet 280, New Series). Memoirs of the Geological Survey of Great Britain, HMSO, London. Maton, W.G., 1797. Observations Relative Chiefly to the Natural History, Picturesque Scenery and Antiquities of the Western Counties of England made in the years 1794 and 1796. Vol. 2, Somerset. W.G. Maton, Salisbury. Mattigod, S.V., A.L. Page and I. Thornton, 1986. Identification of some trace metal minerals in a mine-waste contaminated soil. Soil Sci. Soc. Am. J., 50:254 258. Pooley, G., 1693. An account of digging and preparing the Lapis Calaminaris. Philos. Trans. R. Soc. London, xvii: 672477.