There are a few aspects of plasma that quickly become clear after being introduced to it: it is purple, highly combustible, and (as anyone who's handled a bar of it at room temperature can attest) very poorly named.
There's lots of other interesting and useful properties of plasma that have been teased out with a few years of research and study: its amazing thermodynamic properties, its incredible tensile strength when mixed into alloys, and the immediate toxic effects it has on organic lifeforms when ingested being some of the most notable. These properties have all proven to be extremely useful in a variety of applications, and more importantly, extremely profitable to exploit, making plasma mining and research two of the biggest financial boons in Nanotrasen's entire history.
As the years of research and mining have gone by, however, not all of the information that has come out about plasma has been good. Indeed, some of the most highly classified and secretive research being conducted by NT anywhere is focused on the long-term effects of plasma on humanoids. The short term effects of ingesting plasma in large amounts are clear; it acts as a neurotoxin that causes widespread cell death throughout the victim's body. Luckily, these effects can be avoided with a simple oxygen mask, and it doesn't take a trained surgeon to tell if someone's huffed enough to kill them. Infinitely more insidious, however, are the long term effects. While researchers' understandings of these effects are constantly changing as more research is produced, clear patterns are emerging where affected individuals suffer from gradual neurological decay, decreased attention span, violent mood swings, and most notably, degraded ability to feel empathy for others.
Usually, these findings are laughed off and treated like a joke when first heard. It makes sense: the Spinward Periphery is a perfect storm for seedy and antisocial behavior, and it's not like NT's lax approach to hiring standards is helping things. With all the deceit and skullduggery that the average NT crewmember is exposed to, not to mention the occasional outright bloodbath, some would find it more surprising that any moral code could survive beyond "kill or be killed". But if nothing else, the first several waves of employees proved resilient and resourceful, struggling to maintain some sort of personal normalcy and decency among the chaos they found themselves in.
"These scans from the last group of subjects are astounding. Here, look at this one- it's like the decay is targeted directly at the parts of the brain that help regulate emotions. These are dangerous people, don't forget that when you're dealing with them." --An anonymous veteran researcher, unknowingly studying his own brain scan.
For the many faults that can be levied against NT's management of the Spinward Periphery, its command structure and management selection are remarkably egalitarian. The execs and officers of the first waves of personnel sent to the Spinward Periphery were more than willing to lead from the front and become personally involved in dangerous work when needed, and when it came time to select their successors, they chose from the crewmembers they led in the field. Under intense pressure to deliver from both the corporate offices back home and their colleagues on the Periphery, plus extremely high personnel turnover, traditional barriers to advancement such as ethnicity, gender, and even species took a back seat to credentials and experience in the field. Indeed, while non-humans are still barred from serving as station-side Heads of Staff, as well as being excluded from basic protections in the standard silicon lawsets, every species of humanoid is currently represented in the staff of the higher Spinward Central Command. This isn't to say that things are perfectly egalitarian- discrimination still occurs, and there's still a strict chain of command- but the CentCom staff are generally sympathetic to the crewmembers they administrate and remember their own time in the field when balancing risks.
So when signs of this systemic mental and empathetic decay started cropping up among the CentCom staff, they began to take the reports seriously. As research has since revealed, plasma is much harder to fully purge from an area than previously thought, meaning trace amounts of plasma are often circulated through the stale recycled air onboard the stations unbeknownst to the crew. While this trace exposure isn't enough to cause the outright poisoning medical staff are trained to spot and treat, it is enough to cause decay over long periods of time. Only now, after almost two decades of NT's presence on the Spinward Periphery and several generations of workers and leaders passing through its stations, has the scope of the issue started to become clear.
The intensity of the decay seems to roughly correlate with a crewmember's length of service and time spent in contaminated areas, but some crewmembers seem more susceptible to the decay than others. Preliminary models estimate that anywhere from 10-35% of crewmembers serving more than one month show minor signs of decay, with estimates reaching as high as 80% after one year, but the truth is that no one is sure how widespread it is. The Spinward Periphery truly is hard on people, and the constant stress and trauma thrown at workers combined with the already rough workforce makes it extremely difficult to identify who is suffering from these effects and to what degree.
In the meantime, ongoing research on plasma's long term effects is strictly classified to the highest degree, and NT has not publicly acknowledged the phenomenon. NT's leadership is at a very uneasy crossroads, both highly concerned with the systematic damages their work is causing among the workforce and themselves, but ultimately unwilling to slow down plasma processing until more concrete evidence comes out. Most of the cases appear to be mild so far, and while the decay seems to be resistant to most chemical forms of treatment such as mannitol and neurine, simple cognitive mindfulness exercises have proven useful in offsetting the effects. By being aware of the changes to their mind, patients can still function among more polite society back in Sol, though increased emotional distance and stress when trying to return to their previous lives is very common among ex-crewmembers.
- The effects of the decay are left vague and vary from person to person, perfect for you to fill in how it affects your character as you please. Suffering from decay doesn't have to mean your character loses all self control, perhaps it just causes them to lose perspective sometimes and act very callously in certain situations. Later, when they reflect on what happened or are talking about it with someone else, it may dawn on them how disturbing their actions on a given shift were, and they may take steps to try to control themselves in the future. Maybe it'll work, maybe it won't.
- The ongoing research into the decay is highly classified and hidden from the crew, but perhaps your character has a background in neuroscience or psychiatry, and is involved in the research. Or maybe they have a friend who is involved, or they found concerning research reports on the subject on a superior's desk. There are many ways that your character may have some hazy idea of plasma's long term effects, and thus become aware of the hazards that could come with staying. What is it that keeps them here?
- The described effects of the decay purposely overlap with those of several personality disorders and potential results of extreme trauma. Has your character become a bastard because plasma is warping their brain? Is it a coping mechanism to help them survive the insane amounts of senseless violence and constant stress they've been exposed to? Or have they always been like that inside, and SS13's "survive at all costs" mindset has just given them an excuse to really lean into it? There's no reason it can't be a little of each, and everyone has been a bastard to someone at some point.