Nematodes colonization of pyrite cinders in a phytoremediation study

A phytoremediation programme was applied to a chemical factory site affected by pyrite cinders dumps at Torviscosa (North-Italy). Cinders of pyrite were the residues from production of sulphuric acid and they are extremely contaminated by heavy metals and arsenic. The project focused on the effects of soil amendments and different plant species on phytoremediation efficiency to restore soil health. In this paper we report results about changes in nematodes communities observed in manure treated plots. The experimental trial was prepared as follows: the top cinders layer (20-40 cm) was mixed with the covering soil (0-20 cm) forming a “mixture” that was treated with chemical fertilizers or well-rotted cow manure and then sown with three different metals-accumulating plants: giant reed (Arundo donax L.), sunflower (Helianthus annuus L.) and sorghum (Sorghum bicolor L.). Samples were taken: a) at the initial time on the pyrite cinders and covering soil, separately; b) on the mixture before the application of manure; c) on the mixture cultivated with three species, two months after sowing. Comparison was done on general composition, trophic structure and biodiversity of the nematofauna collected in all the plots. In pyrite cinders nematodes were not detected, probably because of physical properties (heavy silty texture) and high concentration of metals. Highest abundance of nematodes was recorded in sunflower (88 ind/100 g of soil) and lowest abundance was in the mixture before fertilization and sowing (23 ind/100 g of soil). Across all the plots, bacterial feeders were the dominant trophic group ranging between 95.6% in the mixture and 63.7% in sorghum. In these early stages of succession plant feeders were not detected and omnivores were recorded in a low percentage, except for sorghum. In soil covering and in the mixture Cephalobidae was dominant. In the cultivated plots, Rhabditidae was the most abundant family, mainly due to the application of manure. Moreover, in sorghum Diplogasteridae (in particular Butlerius) was 25% of the total community, whereas in sunflower and giant reed did not reach 5% and in the samples collected before the treatments it was not detected. The communities in sorghum seemed to be rather structured, being omnivore-predators quite abundant. The communities in the other cultivated plots were dominated by one family and were not well structured, as demonstrated by Maturity Index and the other calculated Indices. Our results showed that phytoremediation provided to a repopulation of an area extremely compromised. Moreover, analysis of nematofauna could be a useful tool in assessing the degree of soil disturbance and to study the step of the remediation process.