DDT is still a problem in developed countries: the heavy pollution of Lake Maggiore

Abstract

The Zebra mussel (Dreissena polymorpha), one of the most widely used bioindicators of persistent organic pollutants, trace metals and radionuclides in several worldwide freshwater ecosystems, has been used to monitor DDT contamination trends in Lake Maggiore since 1996, caused by industrial effluents on a tributary of the River Toce, one of the major affluents of the lake. Dreissena specimens were collected at two sampling sites, one within the Baveno Bay, where the River Toce flows, and the other outside (Villa Taranto). Total DDT levels (3119.6 ng/g lipids at Baveno and 1351.2 ng/g lipids at Villa Taranto) in the soft tissues of the Zebra mussel decreased at both stations by about 30–50% in the first year after the closure of the chemical plant reaching an almost steady-state condition. The high concentrations measured in Zebra mussel specimens of Baveno Bay in 2000 (1947 ng/g lipids) and the percentage of pp′DDE in comparison with total DDT concentration, which showed a slight increase in the last years, clearly indicate that a contamination source is still present, deriving probably from the lacustrine sediments and the River Toce. Data show that the environmental risk is very high within the Baveno Bay and the recovery time should be longer than in the other parts of the lake, where DDT levels in Dreissena are presently two times higher than those measured in the other Italian subalpine lakes.

Introduction

Persistent organic pollutants (POPs) are highly stable organic compounds used as pesticides in agriculture and in industry, or generated unintentionally as the by-product of combustion and industrial processes. POPs have chemical and physical properties which cause numerous problems to the environment, wildlife and human health: POPs are lipophilic compounds that can bioaccumulate in lipid tissues and, owing to their persistent and semi-volatile nature, can travel long distances and condense over the colder and more remote areas of the world (Kurtz, 1990; Cotham and Bidleman, 1991). As a result of these properties, there is growing concern over the toxic effects of these compounds on biota, in particular on the higher species of the food chain, even at extremely low environmental levels. Some of these chemicals are endocrine disruptors and various dangerous effects such as eggshell thinning, behavioural changes, impaired male reproductive ability and estrogenic activity interfering with sex hormones have been confirmed (Kelce et al., 1995). The problem of endocrine disruptors is one of the five priority research areas established by the Committee on the Environment and Natural Resources of the United States (Kavlock, 1999) and some detailed research strategies have also been put forward by the European Union.

Until the 1970s, DDT was one of the most widely used pesticides in many Western countries, although a number of studies showed several adverse environment effects and a proven hazard to non-target organisms such as fish and birds. Several legislative decrees were ratified in Europe to regulate its use, but no restrictions have so far been set for the production of this insecticide. In Italy, agricultural use of DDT was banned in 1978, excepted for particular applications in floriculture and zootechnics. Recently, a treaty to control, reduce or eliminate discharges, emissions and losses of several POPs was signed by the European Community. The protocol regulates 12 chemicals, of which most are subject to an immediate ban. These include aldrin, chlordane, DDT, dieldrin, endrin, eptachlor, mirex, toxaphene, polychlorinated biphenils (PCBs), hexachlorobenzene, dioxins and furans. Other protocol obligations include the application of best available technology to limit air emissions from major stationary sources of dioxins (PCDDs), furans (PCDFs), HCB and polycyclic aromatic hydrocarbons (PAHs). However, a health-related exemption has been granted for DDT, which is still needed in many countries to control malarial mosquitoes. Similarly, in the case of PCBs, which have been widely used in electrical transformers, governments may maintain existing equipment in a way that prevents leaks until 2025 to give them sufficient time to arrange for PCB-free replacements.

Notwithstanding the legal restrictions governing the use of several POPs in Western countries, some have recently been found in various American and European aquatic ecosystems (Mersch et al., 1992; Bruner et al., 1994; Roper et al., 1996; Hendriks et al., 1998; Gundacker, 1999; Binelli et al., 2001a, Binelli et al., 2001b). Environmental problems of POPs are still persistent, as shown by the detection of DDT contamination in Lake Maggiore in 1996, the second-largest Italian lake by area and volume––an outstanding example of how a pollution problem associated with a chemical whose use, but not production, was banned two decades ago can arise. A previous study conducted in Lake Maggiore (Ceschi et al., 1996) showed very high levels of DDT in several species of fish, beyond the legal limit for edible fish. The commercial fishing of some species in this lake was halted in June 1996. The source of the pollution was traced back to a chemical plant (CIPAIS, 1999), which both produced and discharged DDT over several years into the River Marmazza, a tributary of the River Toce, in turn one of the major affluents of Lake Maggiore (Fig. 1).

We carried out a 5-year biomonitoring operation (1996–2000), using the bivalve Dreissena polymorpha to measure DDT changes in Baveno Bay, where the River Toce flows, and the spread of contamination outside the bay. Wide distribution, continuous availability throughout the year, adequate body size, firm site attachment capability of the bissus, ease of sampling, good salinity tolerance and relatively high longevity make this mollusc particularly appropriate for use as a bioindicator. The Zebra mussel has already been used to assess the contamination of freshwater ecosystems by trace metals (Johns and Timmerman, 1998; Gundacker, 1999), organotin compounds (Becker et al., 1992) and POPs (Mersch et al., 1992; Bruner et al., 1994; Hendriks et al., 1998).