DU ammunition is used for 2 reasons, neither of which have to do with nuclear/radiation based weaponry effects. These make it into a top-performance solution for anti-armor applications. Albeit one with some long term environmental downsides which has caused ongoing R&D and deployment of alternatives in recent years (the exact risks are a matter of debate, but are much amplified by playing on "nuclear" fears):
it is very much heavier than even lead, making it very good at storing kinetic energy over distance and reducing projectile drop
against armor, DU has interesting properties in how the shaped charge "sharpens itself" into the target. Tungsten, in the same weight class, has the opposite behavior, "mushrooming" instead.
Note that Russia also fields DU ammunition on tanks (it is unclear if Russia has used it in Ukraine)
The information that one of the shells has the depleted uranium core was confirmed to TASS by military expert, Editor-in-Chief of the Arsenal of the Fatherland journal Viktor Murakhovsky. "It has the alloy of the depleted uranium and tungsten," he said, adding that the open sources mentioned it as "the Material B."
The use of depleted uranium ammunition does not violate any international treaties, the expert said.
A number of countries have reduced their use of DU. The DU rounds in the Challenger 2 are "legacy rounds", not produced anymore.
Now, depending on who you listen, DU is either no problem BBC:
He said depleted uranium rounds used by Challenger 2 tanks contained only trace elements of depleted uranium.
He added it was "laughable" to suggest depleted uranium rounds were in any way linked to nuclear weapons, which uses enriched uranium.
Be careful when reading on this topic. Almost everyone is going to try to talk risks either up or down, depending on what view they want to promote. For example "only traces", is complete BS (though you might stretch that to claim instead that there is only trace radioactivity). It wouldn't make any sense to have trace quantities of DU since the first benefit, reduced ballistic drop, requires a significant proportion of the projectile to be DU.
Looking at the M1's better documented round, it contains about 6.8kg DU
DU is not particularly dangerous as a primary effect during combat (i.e. you'll be killed by other effects). However, it burns and leaves a dust residue which is environmentally dangerous long term, making it a big problem (again be careful wrt impartiality, this is the International Coalition to Ban Uranium Weapons after all):
The US, UK, Russia, China, France and Pakistan produce uranium weapons. 14 other states are known to at least store uranium weapons. As far as known, these weapons have been used only by two states so far: the US and Britain. Large quantities of DU were fired in Iraq and the Balkans. When DU bullets hit an armored surface, they are burned by the high temperatures generated by the impact. This creates a very fine dust that is radioactive and chemically toxic. Through food and respiration, this toxic dust is absorbed by the body. In the body, the radiation and the chemical poison cause serious damage. Many diseases can be caused: alteration and damage to the genome, malformations of the human body in the womb, impaired fertility in men and women, cancer in almost all organs, kidney failure and behavioral problems.
Bullets that miss their target also corrode very slowly, releasing their toxicity to groundwater and soil, poisoning the environment and humans. The use of DU creates a long-term health threat for civilians and the military alike, obstructs reconstruction through ravaged areas, spreads fear and is difficult and costly to remove. The properties of DU weapons make it impossible to completely decontaminate contaminated sites where they were fired. Even without a special prohibition contract, the use of DU ammunition with its consequences is contrary to applicable standards of international humanitarian law, human rights and environmental protection. This is where ICBUW’s efforts are aimed at banning these weapons and addressing their consequences for humans and the environment. In concrete terms, the distinction requirement of international humanitarian law, the human right to a healthy environment, especially protection against toxic substances, and, in particular, the precautionary principle / approach are violated.
The land the DU ammo will be used on belongs to Ukraine, so it will be their problem and it's their decision.
The rounds being delivered are a standard part of the Challenger 2's existing anti tanks ammo suite and similar rounds are used throughout NATO and indeed by Russia. They are standard anti-tank rounds, even if countries are now trying to limit DU use in upcoming ammunition manufacture. They are not some "custom hellbrew" to be especially mean to Russian soldiers somehow. One can certainly be of the opinion that DU use should be limited to high-intensity warfare of critical importance, but they are part of the toolset in those circumstances.
The environmental risk is a trade off Ukraine is aware of and willing to tolerate in this instance. For rather obvious reasons.
Remember, these are large 120mm shells used for tank-on-vehicle direct fire. They will be used, for sure, but they won't be shot at high volume throughout the country side. And remember too that the actual level of toxicity is a matter of some debate.
Short term radiological effects are immaterial and pure Russian disinformation but certainly are useful to Russian information campaigns.
And, in any case, as far as Ukraine is concerned, residual DU will be one of many, many, problems they will be facing, environmentally, so I rather doubt it will count for all that much.
When a range of munitions have been used, soil toxicity can be persistent and challenging to remove so locations must be prioritised depending on the level of damage, says Hinwood. Excessive bombing in places like Mariupol, a port city with multiple types of industry and urban development, poses enormous challenges in terms of crop remediation, she says. "If you have damage to urban infrastructure, wastewater infrastructure, maybe chemical manufacturing plants, you've got multiple environmental impacts there," she says.
And that's before one gets into Russia's use of cluster bombs and anti-personnel mines (Russia has not ratified the Ottawa Treaty banning them, but Ukraine has).
More on the state of DU in 2022:
p.p.s. when reading about DU, keep in mind that any reference to Gulf War Syndrome can be ignored, as the cause for that has recently been determined to be sarin.
* (based on .627 * (.027 /2) * (.027/2) * 3.14 *19000 kg/m3 volume for a 627mm long 27mm diameter DU penetrator)