**6. Conclusions**

In this paper, we argue that trade policy should be assessed in light of the impact on sustainability and sustainable development strategies. The empirical evidence shows that the GL index is more intense among countries with high eco-innovation index, unlike those with a lower eco-index. This result is very important because there is a link between eco-innovations and trade, as demonstrated by Roy in 2017 [6]. For this reason, the adoption of measures aiming at improving the transition to eco-innovation (such as diffusion of green technologies or environmental certification) will improve the intra-industry trade favouring the whole economic performance. Constantini et al. (2017) [48] found that eco-innovations seem to be able not only to directly reduce pollution, but also to foster overall environmental performance via market transactions, both domestically and internationally. In our article, the Grubel–Lloyd Index does not show whether the eco-innovation is an effective way of favouring the transition to a low-carbon sustainable economy, or whether it relates to the degree of environmental pollution or environmental damage differences among sectors (as shown in other recent studies), but it illustrates that eco-innovation can be a driver to incentivise the intra-industry trade without compromising on the increasing greenhouse gas emissions, climate change, land degradation or energy consumption which characterise trade growth. To summarise, the Grubel–Lloyd Index is a proxy indicator of the eco-index. In the centre of our views, is the fact that it is the spread of environmental technologies what matters, and it happens in all sectors, thus a

division in polluting/non-polluting sectors does not contribute much to the development of our ideas. Moreover, a rigorous sector-by-sector analysis seems for now not to be a feasible task, because of the scarcity of data; even for the EU data exist only for a limited number of countries (see [49]). Therefore, even an indirect measure, such as the one we propose, has the potential to be useful.

These results are strategic for helping to disseminate eco-innovations, and green knowledge among countries. Therefore, identifying clearly specific needs and barriers is a fundamental precondition to fostering the development and transfer of eco friendly technologies [50]. Environmental issues have been discussed in the scope of international trade in general—trade can lead to growth, and therefore to greater environmental awareness [51]. This study shows that the eco-innovation contributes to sustainability as a direct measure, but at the same time it is an incomplete indicator. A trend to investigate "eco-innovation–IIT interrelation" is emerging, because the existing indicators for measuring international trade can no longer be just a neutral mechanism for confirming or rejecting the sustainable welfare. IIT enhances sustainability, but IIT differs for goods and diffusion of innovations due to higher varieties in different countries. Our study helps to enrich the limited volume of empirical studies similar to the present and creates opportunities for new research.

**Author Contributions:** Introduction: V.D.; Literature review: T.G. and G.M.; Methodology and data: G.M.; Results: V.D., G.M. and T.G.; Discussion V.D., G.M. and T.G.; Conclusions: T.G. and V.D.

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

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