Italy, Seveso e Meda (Monza e Brianza), Lombardia, Italy

Seveso (ICMESA accident)

On 10 July 1976 a reactor at the ICMESA chemical plant in Meda released a cloud carrying an estimated 15–30 kg of TCDD, the most toxic dioxin, over about 18 km² of Brianza. It is the accident that gave its name to the European directives on industrial hazards, and the exposed population has been followed for almost fifty years.

Dioxins and furans

Status: Contained
Area: 1,800 ha on land¹
Activity: until 1976
People affected: 736 (1976)²
Media: soil, living organisms
Kind of site: chemical works, accident

Area. About 18 km² reached by the cloud (Eskenazi et al. 2018), divided into zones A, B and R by decreasing soil contamination. Clean-up by soil removal covered 43 hectares, now the Bosco delle Querce park.
People affected. Residents evacuated from zone A (212 families). Zone B about 5,000–6,000 inhabitants, zone R about 32,000 (Eskenazi et al. 2018; Bertazzi et al. 2001).

Contaminants

Organic compounds

Dioxins and furans

Status

Contained

The soil of the most contaminated zone has been sealed since 1984 in two basins under the Bosco delle Querce park. Residual dioxin has been found in the land along the route of the Pedemontana motorway: the clean-up of about 100,000 m² was planned by lots, with verification sampling carried out jointly with ARPA Lombardia (Pedemontana documents, January 2026).

Story

In 1945 ICMESA applied for permission to build a plant in Meda, which grew through the 1950s and 1960s. Among other things it made 2,4,5-trichlorophenol. On Saturday 10 July 1976, at 12:37, a runaway reaction released an aerosol that settled to the south-east, mainly over Seveso. In the following days people reported nausea, headaches and eye irritation; 19 children were admitted to hospital with skin lesions and nearly 200 cases of chloracne were recorded, mostly in children.

The territory was divided into three zones according to TCDD measured in soil: zone A (mean values between 15.5 and 580 µg/m²), zone B (1.7–4.3 µg/m²) and zone R (0.9–1.4 µg/m²). The 736 residents of zone A were evacuated between 26 July and 2 August; restrictions were imposed in zones B (about 5,000–6,000 inhabitants) and R (about 32,000).

Analyses in 1976, 1977 and 1980 showed that 95% of the dioxin had stayed in the top 25–30 cm of soil. The clean-up consisted of removing the soil, in one to three passes of about 30 cm depending on contamination: 43 hectares, 46 cm average depth, about 200,000 m³. Soil, rubble from the demolished houses and other residues were sealed in two basins built between 1982 and 1984, one in Seveso of 200,000 m³ and one in Meda of 80,000 m³, isolated by four successive barriers. Clean soil was brought in and a wood was planted on top: about 5,000 trees and 6,000 shrubs, the Bosco delle Querce.

The matter reopened with the Pedemontana motorway, whose route crosses land in the former contaminated zones. Surveys in 2009, 2012 and 2016 found dioxin above the legal limits in delimited areas; the company prepared a clean-up by excavation over about 100,000 m², divided into lots, with 908 verification samples planned.

Timeline

194529 November: ICMESA applies for permission to build the Meda plant.
197610 July: the TCDD cloud escapes from the reactor; zone A is evacuated between 26 July and 2 August.
1982Construction starts on the two basins at Seveso and Meda, finished in 1984.
1986The monitoring network for the basins is installed; the Bosco delle Querce grows on the area.
1996The Seveso Women's Health Study begins.
2009First soil survey along the Pedemontana route: dioxin above the limits in delimited areas.
2016Shallow, intermediate and deep borings along the future motorway route.

Health

Population cohort studies (Bertazzi, Consonni, Pesatori; 278,108 people across the contaminated zones and the reference territory). Mortality 1976–2001: no increase in all-cause mortality; excess of lymphatic and haematopoietic cancers in zones A (RR 2.2; 95% CI 1.0–5.0) and B (RR 1.6; 95% CI 1.1–2.3); after twenty years, all-cancer mortality in zone A RR 1.6 (95% CI 1.0–2.6). Cancer incidence 1977–1996: no difference for all cancers combined; lymphohaematopoietic cancers in excess in zone B (29 cases; RR 1.56; 95% CI 1.07–2.27); breast cancer in zone A women 15 years or more after the accident (5 cases; RR 2.57; 95% CI 1.07–6.20); no soft-tissue sarcoma in zones A and B.

Seveso Women's Health Study (981 women aged 0–40 in 1976, with TCDD measured in serum collected at the time; median 55 ppt): per ten-fold increase in serum TCDD, breast cancer risk at twenty years HR 2.1 (95% CI 1.0–4.8) and all-cancer incidence at 32 years HR 1.8 (95% CI 1.3–2.5); 25% longer time to pregnancy and almost double the odds of infertility. Among births in zone A in 1977–1984 an excess of girls (48 against 26 boys); higher neonatal TSH in babies of mothers from zones A and B; lower sperm concentration in sons exposed in the womb.

Remediation

1977excavationRemoval of contaminated soil over 43 hectares, in one, two or three passes of about 30 cm depending on the dioxin level (average depth 46 cm, about 200,000 m³); demolition of the houses in zone A.
1984containmentTwo containment basins with four successive barriers: Seveso (200,000 m³) and Meda (80,000 m³), built in 1982–1984.
1986revegetationClean soil brought in and about 5,000 trees (oaks, maples, hornbeams, Scots pine) and 6,000 shrubs planted: the Bosco delle Querce. This is restoration on imported soil, not phytoremediation.
2026excavationExcavation of soil with residual dioxin along the Pedemontana route (about 100,000 m², eight functional lots), with excavation floor and wall samples analysed jointly with ARPA.

From the literature

Species that acted on one of this site's contaminants in at least one study. The list is automatic and takes no account of this site's soil, concentrations or climate.