They were discussing the Army developing bullets made out of tungsten and nylon instead of lead with copper jackets.
Tungsten is proving to be anything but "green". Several compounds linked to it may be far more dangerous in lower concentrations and more active in the environment than lead. They may be hazardous and responsible for cancers such as leukemia. However it has not been studied that much in its various compounds, and those which it breaks down into in the environment. So knowledge on those things is still a work in progress.
It may however turn out to be far more toxic than lead in the environment.
They emphasized they were not giving up on effectiveness either. Seems it would be tough creating the weight and impact deformations of lead but hey this is the twenty first century so I guess it is possible.
This is the military remember. They do not allow expanding projectiles. So deformation is not as important. If the round is designed with fracture points it can yaw and fragment in tissue as the SS109 currently does.
For civilian purposes though it would at best be similar to a FMJ (with higher ricochet risk due to hardness.)
Tungsten usualy costs from 8-12x more than lead per pound and is a much less abundant ore, so it is definately only suitable for special purposes, like when high penetration is necessary.
So a plinking ammo or self defense ammo it is definately not.
Further tungsten can cost even more in a finished product because shaping tungsten is very hard on tools since it is one of the hardest materials. So the cost of finished products made of tungsten can greatly exceed the price of raw tungsten.
It is also about 1.7x heavier than lead, so the same weight tungsten makes fewer bullets with a higher BC. Which means a bullet of similar size would actualy cost around 20x what a lead bullet does in material alone, and several times more to shape it into a bullet. Lead is very soft and cheap to mold, causing almost no wear on the machinery that does it. Tungsten however causes significant wear on the tools that shape and work with it, and they require a lot more maintainence which must also be passed on to the consumer.
The same thing would work with iron and nylon to make cheap bullets even if they had a poor BC due to low density. For practice and plinking they could be very helpful. Scrap iron is far cheaper than lead. However
they are currently banned for most civilian use because they qualify as armor piercing handgun rounds under federal law if made out of iron/steel or tungsten. Also if not made to high standards with a thick uniform coating of nylon the rifling could touch the very hard metal and greatly increase barrel wear, especialy since something like tungsten is harder than the steel of the barrel.
So all around, it is unlikely you will see many of such rounds in the future. They will definately not be replacing lead except in special uses where the significantly higher cost and special properties of tungsten is desired.