THE HISTORY OF LARGE-SCALE ATMOSPHERIC LEAD POLLUTION IN SWEDEN

Ingemar Renberg, Maja-Lena Brännvall, Richard Bindler (Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden); Ove Emteryd (Department of Forest Ecology, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden)

Corresponding author: Ingemar.Renberg@eg.umu.se

ABSTRACT

Analyses of lead concentrations and ²⁰⁶Pb/²⁰⁷Pb isotope ratios of sediment cores from >30 lakes, peat cores from three bogs, and soil profiles from 11 sites have been used to study atmospheric lead pollution history in Sweden. The first signs of atmospheric lead pollution date to about 3500 years ago. There was a small, but clear peak during the Greek-Roman period around 0 AD. About 1000 AD a major increase occurred, and this was the starting time for the modern lead pollution era. With the Industrial Revolution atmospheric lead pollution increased, however, not as much as usually suggested. Lead pollution increased markedly after World War II, peaked about 1970, and has since declined. The geographic distribution of pre-industrial pollution was similar to the contemporary pattern with a strong south to north gradient. The lead records of the sediment and peat deposits reflect the history of mining and metal production in the old World and signals large-scale transport of air pollution from continental Europe and the British Isles to Scandinavia already in pre-industrial time. The cumulative lead pollution load, of which 50% came in pre-industrial time, is 2-5 g per m² ground surface in southern and about 1 g in northern Sweden.

INTRODUCTION

This paper summarises nearly ten years of research on the long-term history of atmospheric lead pollution in Sweden, northern Europe. It is based on analyses of stable lead isotopes and lead concentrations in sediment cores from >30 lakes and peat cores from three ombrotrophic bogs. The sites are distributed all over the country and span a south-north distance of about 1000 km (56 ^oN to 67 ^oN)

METHODS

Sediment and peat cores cover typically >5000 years and were sampled using appropriate corers (gravity corer, freeze corer, Russian peat corer, Wardenaar corer). ICP-MS was used to analyse lead concentrations and ²⁰⁶Pb and ²⁰⁷Pb isotopes. Uncertainty of the analyses are <10% for concentrations and <0.5% for isotopes. Lead pollution concentrations in the sediments (total minus natural) were calculated using isotopes and a simple mixing model. Chronologies are based on radiocarbon dating and sediment-varve counting.

RESULTS AND DISCUSSION

²⁰⁶Pb/²⁰⁷Pb ratios have proven to be particularly useful for distinguishing pollution lead from natural geological lead in the Swedish environment, because of the very large difference in ratios between uncontaminated soils/sediments and airborne lead pollution. Deep soil horizons and old sediments have a ratio >1.3 (mean 1.55 ± 0.29; n=46 sites), while early lead pollution from metal production (pre-1900) had a ratio typically about 1.17, and modern airborne lead pollution an even lower ratio (for references see Bindler et al 1999, Brännvall et al. 2000a).

Figure 1. Temporal trends in atmospheric lead pollution in Sweden. Lake Kassjön and Koltjärn (N Sweden) have varved sediment and higher time resolution than Lilla Öresjön (S Sweden). Redrawn from Renberg et al. (2000).

Temporal trends of atmospheric lead pollution

All cores show very similar pollution trends (Brännvall et al. 1997, 1999, 2000a). As an illustration, Figure 1 shows pollution concentrations in the sediments of a southern Swedish lake (Lilla Öresjön) and a northern Swedish lake (Kassjön) (Renberg et al. 2000). For more details about the pollution history of Kassjön, which has varved (annually-laminated) sediment, see also Brännvall et al., this conference.

1. The first indication of an impact of non-catchment, airborne lead dates to 3,500-3,000 years ago in the peat bogs and in some south Swedish lakes with low natural lead concentrations and high ²⁰⁶Pb/²⁰⁷Pb ratios (Brännvall et al. 1997).

2. The large world production of lead during Greek and Roman cultures 2000 years ago caused widespread atmospheric lead pollution (Settle & Patterson 1980, Nriagu 1983). In sediments in southern Sweden total lead concentrations increased from about 7 mg g^-1 dry sediment (background concentrations) to about 20 mg g^-1, and in northern Sweden from 7 to 11 mg g^-1. This Greek-Roman pollution peak has been detected in sediments and peat from several European countries, as well as in Greenland ice (Shotyk et al. 1998, Hong et al. 1994).

3. Between 400 and 900 AD the deposition rate of atmospheric pollution was lower, but at the end of the 10^th century it increased markedly, following the expansion of mining and metal production in Europe. Lead concentrations in sediments of South Swedish lakes often reached >50 mg g^-1. The pollution level 1200 AD was about 35% of the level in the 1980s when atmospheric lead pollution was near its all-time high.

4. The four varved lake sediments studied show pollution peaks 1200, a trough 1350, a peak 1530, and a trough in the 17^th century (Brännvall et al. 1999). These changes coincide remarkably well with the economic history of Europe, see Brännvall et al., this conference.

5. Lead pollution levels increased with the Industrial revolution, however, not as much as usually assumed. The real increase in modern time followed after the Second World War with increasing fossil fuel combustion and particularly with the use of leaded petrol for vehicles. In Sweden atmospheric lead pollution has declined markedly since the 1970s and it is at present below the 1530s level.

Figure 2 Pollution lead concentrations in sediments from about 0 AD and 1200 AD, and total lead concentrations about 1600 AD and in the 1980s. Redrawn from Brännvall et al. (2000a).

Pollution sources and the geographic distribution of atmospheric lead deposition

Figure 2 shows pollution conditions about 0 AD, 1200 AD, 1600 AD, and in the 1980s (Brännvall et al. 2000a). There is a strong south to north pollution gradient. The geographic distribution of the Greek-Roman (0 AD) and the Medieval (1200 AD) pollution over Sweden is very similar to the present-day pollution map, and was caused by long-range, south-to-north atmospheric transport. The acid rain issue, discovered in the 1960s, first drew the attention to this large-scale transport that carries emissions from industrial areas in continental Europe and Great Britain to Scandinavia.

Cumulative loads of atmospheric lead deposition

The lake sediments allow estimates of the relative cumulative loads of pollution in pre-industrial and industrial times, respectively. Even though the annual atmospheric flux of lead was very high from the 1950s to the 1980s, the amount deposited during the Industrial period (1800 to the present) is only approximately 50% of the total cumulative load of pollution lead (3500BP to the present). The total cumulative load of lead pollution through time can also be determined in soils. Analyses of soil profiles from 11 boreal forest sites (Brännvall et al 2000b), as well as a whole-basin study of a lake, show that 2-5 g pollution lead per m^-2 ground surface has accumulated in southern Sweden and about 1 g m^-2 in northern Sweden. This lead has penetrated 20-60 cm into the soil profile, and most is accumulated in the B-horizon (Bindler et al. 1999, Brännvall et al. 2000b).

REFERENCES

Bindler R, Brännvall M-L, Renberg I, Emteryd O, Grip H (1999), Environ. Sci. Techol. 33: 3362-3367.

Brännvall M-L, Bindler R, Emteryd O, Nilsson M, Renberg I (1997), Water Air Soil Pollut. 100: 243-252.

Brännvall M-L, Bindler R, Emteryd O, Renberg I (2000a). J. Paleolim. In print.

Brännvall M-L, Bindler R, Emteryd O, Renberg I (2000b), Water Air Soil Pollut. In print.

Brännvall, M-L, Bindler O, Renberg I, Emteryd O, Bartnicki J, Billström K (1999), Environ. Sci. Technol. 33: 4391-4395.

Brännvall M-L, Bindler R, Renberg I, Emteryd O (this conference), The power of varved lake sediments for high-resolution studies of pollution history.

Hong S, Candelone J-P, Patterson CC, Boutron CF (1994), Science 265: 1841-1843.

Nriagu J (1983) Lead and Lead Poisoning in Antiquity. Wiley, New York.

Renberg I, Brännvall M-L, Bindler O, Emteryd O (2000), Ambio 29: 152-158.

Settle D & Patterson CC (1980), Science 207: 1167-1176.

Shotyk W, Weiss D, Appleby PG, Cheburkin K, Frei R, Gloor M, Kramers JD, Reese S, Van der Knaap WO (1998), Science 281: 1635-1640.