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Geospatial Health 8(1), 2013, pp. 77-86 A spatial, statistical approach to map the risk of milk contamination by β-hexachlorocyclohexane in dairy farms Sabrina Battisti1, Antonino Caminiti1, Giancarlo Ciotoli2,3, Valentina Panetta4, Pasquale Rombolà1, Marcello Sala1, Alessandro Ubaldi1, Paola Scaramozzino1 1Istituto Zooprofilattico Sperimentale delle Regioni Lazio e Toscana, Rome, Italy; 2Istituto Superiore per la Protezione e la Ricerca Ambientale (ISPRA), Rome, Italy; 3Dipartimento di Scienze della Terra, Università di Roma “Sapienza”, Rome, Italy; 4L’altra statistica srl, Rome, Italy Abstract. In May 2005, beta-hexachlorocyclohexane (β-HCH) was found in a sample of bovine bulk milk from a farm in the Sacco River valley (Latium region, central Italy). The primary source of contamination was suspected to be industrial discharge into the environment with the Sacco River as the main mean of dispersion. Since then, a surveillance programme on bulk milk of the local farms was carried out by the veterinary services. In order to estimate the spatial probability of β- HCH contamination of milk produced in the Sacco River valley and draw probability maps of contamination, probability maps of β-HCH values in milk were estimated by indicator kriging (IK), a geo-statistical estimator, and traditional logistic regression (LR) combined with a geographical information systems approach. The former technique produces a spatial view of probabilities above a specific threshold at non-sampled locations on the basis of observed values in the area, while LR gives the probabilities in specific locations on the basis of certain environmental predictors, namely the distance from the river, the distance from the pollution site, the elevation above the river level and the intrinsic vulnerability of hydro-geolog- ical formations. Based on the β-HCH data from 2005 in the Sacco River valley, the two techniques resulted in similar maps of high risk of milk contamination. However, unlike the IK method, the LR model was capable of estimating coefficients that could be used in case of future pollution episodes. The approach presented produces probability maps and define high- risk areas already in the early stages of an emergency before sampling operations have been carried out. Keywords: beta-hexachlorocyclohexane, geostatistical analysis, indicator kriging, bulk milk, Italy. Introduction ried out an intensive monitoring programme according to which samples of bulk milk were repeatedly taken In the event of environmental contamination, the iden- from all the dairy farms along the valley (Battisti and tification of the polluted area is essential to support Sala, 2007, Sala et al., 2012). Afterwards, the presence actions aimed at the protection of the public. In 2005, of β-HCH was demonstrated also in soil, river and under the environmental monitoring required by human blood in the area downstream of an industrial Directive 96/23/CE, a sample of bulk milk from a farm plant that was considered to be the primary source of in the Sacco River valley (Latium region, central Italy), pollution. In the past, this industry was involved in the was found contaminated by beta-hexachlorocyclohexa- production of “lindane”, an insecticide of which β-HCH ne (β-HCH), a toxic molecule classified as potentially is a by-product. The lower section of the river was clas- carcinogenic by the International Agency for Research sified as the secondary source of pollution as it provided on Cancer. The analytical value was about 20 times the means for distributing the pollutant from the pri- higher the legal limit set at 0.003 mg/kg (DLgs mary source into a larger segment of the environment. 158/2006, Reg. (EC) No 149/2008). A subsequent inves- As many other persistent organic pollutants (POPs), tigation showed the presence of β-HCH in milk and β-HCH is resistant to natural degradation, persists for crops of numerous farms nearby. During the response several years in soils and sediments (Calvelo Pereira et phase of the emergency, with the purpose to outline the al., 2006; Waliszewski et al., 2008; Abhilash and spread of the pollution, the local health authorities car- Singh, 2009) and accumulates in vegetables and ani- mal tissues. Mammal intake of β-HCH occurs mainly Corresponding author: through the diet and the contaminant is excreted with Paola Scaramozzino milk (Hanaoka et al., 2002; Lee et al., 2007; McGraw Istituto Zooprofilattico Sperimentale delle Regioni Lazio e Toscana and Waller, 2009). Bovine milk has been recognised to Via Appia Nuova 1411, 00178 Rome, Italy Tel. +39 06 7909 9472; Fax +39 06 7934 0462 be an excellent bioindicator of different types of con- E-mail: [email protected] tamination (Mamontova et al., 2007; Nuñez et al., 78 S. Battisti et al. - Geospatial Health 8(1), 2013, pp. 77-86 2012; Perugini et al., 2012) and, due to bioaccumula- downstream of the suspected industrial plant as far as tion in animal fat, it is a sensitive indicator of envi- the confluence of the Sacco River and the Liri River ronmental pollution, especially when compared to (Fig. 1). The valley is oriented in the north-west to non-biological media, such as air, soil or water south-east direction and bordered by the Ernici- (Rombolà et al., 2012). Analysis of previous data indi- Simbruini and the Lepini mountain chains. The geolo- cates a statistical association between the contamina- gy of the study area is typical of the whole Central tion of cow’s milk and the use of fodder crops irrigat- Apennines, characterised by a stratigraphic continu- ed with water drawn from nearby rivers (Sala et al., ous sequence of rocks of the carbonatic platform 2012). Although the use of irrigated crops has been (Triassic-Paleocene). This carbonate platform identified as an important risk factor for milk con- sequence is overlaid by Miocene sediments of carbon- tamination, this study focuses on other environmental ate and siliciclastic nature. On the top of these layers, factors, e.g. vegetables absorbing pollutants directly quaternary volcanic rock alternates with alluvial from polluted soil. deposits and travertine facies. Some of these rocks are In recent years, developments and diffusion of geo- characterised by high intrinsic hydro-geological vul- graphical information systems (GIS) as well as the nerability to pollution as: calcareous rock, calcarenite, increasing knowledge in geostatistical methods have travertine and gravelly alluvial deposits (Boni et al., offered researchers advanced instruments to study 1986; Di Loreto et al., 2007). environmental contamination in different settings The Sacco River valley has a rich agricultural her- (Kleinschmidt et al., 2000; Clements and Pfeiffer, itage and a developed dairy breeding sector. Cattle are 2009; Lin et al., 2010). Among other techniques, indi- usually fed with local fodder (pasture and silage) as cator kriging (IK) is a geostatistical tool which esti- well as industrial feed. The human population is con- mates the probability of a contaminant to exceed spe- centrated in residential centres located in proximity of cific threshold concentrations in not sampled locations the river. on the basis of data from surrounding areas, thus pro- viding a probability map of spatial contamination Data sources and description (Van Meirvenne and Goovaerts, 2001; Brus et al., 2002; Ciotoli et al., 2007; Huang et al., 2007; Chu et The full set of results on β-HCH concentrations in al., 2010). On the other hand, classical statistical bovine milk samples collected in the study area in 2005 methods such as logistic regression (LR) combined was extracted by the Information System of “Istituto with GIS have been used for the same purpose based Zoooprofilattico Sperimentale delle Regioni Lazio e on the presence of some environmental predictive fac- Toscana” (IZSLT). All samples with a concentration of tors (Liu et al., 2005; Twarakavi and Kaluarachchi, β-HCH >0.0005 mg/kg to 4% of fat were considered 2005; Lin et al., 2011). positive, even though this value is far below the current Taking these different approaches into considera- legal limit of 0.003 mg/kg to 4% of fat (DM tion, together with information collected during the 27/8/2004). This threshold is sufficiently higher than 2005 crisis in the Sacco River valley, the present study the instrumental limit of detection (LOD), which is was undertaken with the aim to investigate on spatial 0.0003 mg/kg and was chosen as a signal of contami- contamination of β-HCH in bovine milk produced in nation and not of risk, as this concentration in milk is dairy farms in this area. The specific objectives includ- not hazardous to the health of consumers. ed the creation of two probability maps, one using IK The concentration of β-HCH in milk samples was interpolation and another based on the results of a measured by gas chromatographic analysis using an multivariable LR in combination with GIS functions, electron capture detector (ECD), model 7890A from flowed by the comparison of these two maps to high- Agilent Technologies (Santa Clara, USA) with positive light differences and similarities. results confirmed by a TRACE GC gas chromato- graph equipped with a mass-selective POLARIS Q Materials and methods ion-trap detector (ITD-LRMS) from Thermo Electron Corporation (Austin, USA). Study area Data from 54 of the 283 farms sampled in the area were excluded from this study because farmers used to The study area, located in southern Latium about 60 feed animals with fodder crops irrigated with river water km from Rome, comprises the Sacco River valley as this factor is recognised an important risk factor for including the municipality of Colleferros. It stretches milk contamination (Sala et al., 2012). These results S. Battisti et al. - Geospatial Health 8(1), 2013, pp. 77-86 79 Fig. 1. Study area and dairy farms in Latium, Italy sampled in 2005. were removed from the dataset in order to exclusively Vulnerability, a hydro-geological characteristic of evaluate the effect of other environmental variables on soil indicating the susceptibility of groundwater to the spatial contamination of milk.