*4.5. Enrichment Factors*

The magnitude and spatial extent of human-induced change was determined by expressing current normalized to Al metal contents as enrichment over pre-anthropogenic or background levels through the widely used Enrichment Factor (EF) [53,64]. The EF is estimated according to the formula:

$$\text{EF} = \frac{(\text{element/} \text{\AA} \text{\bot}) \text{sample}}{(\text{element/} \text{\AA}) \text{background}} \tag{2}$$

For the calculation of the local background levels, the median elements values of the deeper part (30–37.5 cm) of the core were used. The sedimentation rate in the lagoon, estimated in another core obtained from station A4 by 210Pb analysis, is 0.3 cm·y<sup>−</sup><sup>1</sup> [23]. Thus, the 30–37.5 cm sediments interval corresponds to accumulations more than 100-years old, i.e., well before the urbanization of the study area. Additionally, those sediments had a light brown color, are thus considered as being oxic, and no apparent authigenic accumulations were observed. The metal contents used as the local background were: 38 mg·kg−<sup>1</sup> for Cu, 104 mg·kg−<sup>1</sup> for Zn, 25 mg·kg−<sup>1</sup> for Pb and 0.69 mg·kg−<sup>1</sup> for Cd. These values are similar to the upper boundaries of the 2N HCl extractable metal contents reported by Voutsinou-Taliadouri [65] at the unpolluted, Kerkyra strait, i.e., the marine area between the island and NW Greece: 3–30 mg·kg−<sup>1</sup> for Cu, 7–24 mg·kg−<sup>1</sup> for Pb and 21–94 mg·kg−<sup>1</sup> for Zn. Therefore, the levels proposed here are considered as the best approximation of the local background levels.

Interestingly, the local background for Cd is twice higher than the average shale (0.3 mg· kg−1) reported by Turekian and Wedepohl, [66], and almost 8 times higher than the value of upper continental crust (0.09 mg·kg−1) [67]. A possible reason for this discrepancy is that phosphate bearing limestones, which outcrop in Kerkyra Island, have been found to contain significant amounts of Cd as impurities [68].

Enrichment factors of 1.5–3, 3–5, 5–10 and >10 times are classified as minor, moderate, severe and very severe modification, respectively [69]. The median values of EFs for the anthropogenic metals were low, falling within the range of minor contamination (Cu: 1.1; Zn: 0.9; Pb: 0.9; Cd: 1.4). However, the maximum values of EF for Cd (5.7 at station A5; 3.5 at station A4; and 3.4 at station A3; see elevated Cd/Al values in Figure 6), indicate moderate anthropogenic modification, confined in localized areas of the lagoon. There are no industries located at the wider area of the lagoon that could explain this enrichment. Considering the land uses of the Antinioti drainage basin, Cd may partly derive from phosphate fertilizers that are applied in the adjacent cultivated areas. Another possible source of these metals could be the leaching of solid wastes improperly disposed at the riparian area. Nevertheless, the incidence of high levels in sediments, the suspended matter and the dissolved phase close to the freshwater seepage sites (e.g., A5, A8, A13), complicates further the source apportionment. So far, our results sugges<sup>t</sup> that the freshwater inputs contribute significantly to Cd contamination. Yet, it is unclear whether the percolating water through the karstic formations becomes enriched by anthropogenic activities throughout its flow path prior to its discharge into the lagoon, or it becomes enriched by leaching of bedrock, or other complex geochemical processes.

In the core sediments, EFs ranges were 0.7–1.4 for Cu, 0.7–1.2 for Zn, 0.1–4.1 for Cd and 0.6–10 for Pb. The vertical distributions of EFs, i.e., the evolution of contamination, are similar to the profiles of elemental ratios to Al shown in Figure 7. The highest EF values for Pb were recorded at distinct sediment layers, consistent with the distinct contamination events discussed previously. The highest EF values for Cd correspond to the thick sediment layer at the top 20 cm of the core that is influenced by diagenetic alterations; thus this should not be attributed entirely to contamination. The values of EF for Cu and Zn, remained low and rather constant in time.
