**5. Conclusions**

The study shows that Fe, Ti, V, Ni, Cr, and Co were mainly of lithological origin, although a contribution of anthropogenic sources was not negligible for V, Ni, and Cr. As, Hg, Pb, Zn, Cd, and Cu arose mostly from anthropogenic activities, being related to industrial activities, fuel combustion, and application of organic amendments to soil. Mn seems to have a combined origin (lithogenic and anthropogenic).

Ti and V, having a common origin, showed the same distribution among the studied districts. Furthermore, Ni, Cr, and Co, associated with ultramafic rocks, showed a similar spatial distribution.

The pseudo-total concentrations of Cr and Ni were above the maximum allowable concentrations (MAC) for agricultural soils in 12% and 22% of samples, respectively, while the concentrations of Cu, Pb, and Zn rarely exceeded the MAC values. The pseudo-total V concentration always exceeded this MAC. For the other elements, the concentrations were below the MAC.

The enrichment factors (EFs) showed no anthropogenic enrichment for Ti. There was minimum enrichment of most samples in Co, Mn, As, Cd, Cr, Cu, and Ni, but outliers reached moderate enrichment in Co, Mn, and As, and significant enrichment in Cd, Cr, Cu, and Ni. There was significant enrichment in V, while for Pb, Zn, and Hg the median values denote moderate enrichment, but outliers reached significant enrichment in Zn and extremely high enrichment in Pb and Hg.

The concentrations of bioavailable forms of metals (including some usually considered as lithogenic) were quite often above acceptable thresholds, suggesting a recent enrichment from anthropogenic sources. The toxicity limits for bioavailable Cd, Ni, Mn, and Pb were exceeded by 14%, 10%, 39%, and 56% of samples, respectively.

The results of this study may be valuable for the authorities to issue guidelines for better management of the urban agriculture activities underlining the most toxic elements as well as their safety limits.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2076-3298/7/6/43/s1, Table S1: Concentrations of potentially toxic elements in urban soils of Havana. Raw data.

**Author Contributions:** Conception and design of the work: J.M.M.-A. and R.O.-G. Acquisition of data: J.M.M.-A. Analysis and interpretation of data: J.M.M.-A., R.O.-G. and M.L.F.-M. Drafting the work and revising it critically for important intellectual content: J.M.M.-A. and M.L.F.-M. Final approval of the submitted version: J.M.M.-A. and M.L.F.-M. Agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved: J.M.M.-A. and M.L.F.-M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The first author thanks the Banco de Santander for granting a USC-Banco Santander fellowship, which has made possible the completion of this work. The authors thank Timoteo Caetano Ferreira for revising the manuscript and three anonymous reviewers for their valuable suggestions and constructive criticism.

**Conflicts of Interest:** The authors declare no conflict of interest.
