BOSTON (SHNS) - Reforms in a bill that could clear the Legislature Thursday would "dramatically" improve efforts to monitor street-level drug supplies for dangerous contaminants, according to one expert. As lawmakers prepare to send Gov. Maura Healey a wide-ranging substance use disorder accord designed to help better respond to the opioid crisis, harm reduction specialists praised the measure's focus on limiting legal liability for drug testing. A collaboration between Brandeis University researchers, the Department of Public Health and local partners known as the Massachusetts Drug Supply Data Stream, or MADDS, works to monitor drug supplies in several Massachusetts municipalities, hoping to better alert users about risks they face and inform policy responses. But under existing law, participants can only offer drug-checking services in communities where they have explicit agreements with local law enforcement, according to Traci Green, who leads MADDS. "All of our agreements are at the town [level], with the police department, or at the district attorney level, so we have kind of a patchwork quilt of what we can do where," Green said. The bill that emerged from House-Senate negotiations Tuesday would limit legal liability for harm reduction workers who use drug-testing equipment to examine someone's personal drug supply on the premises of a harm reduction facility, which Green said ensures they would "not have to worry that this was an illegal activity." When drug users have a clearer understanding of how their supply might be tainted, especially involving potent contaminants such as xylazine and fentanyl, they can take additional precautions to limit the chance of a deadly overdose, supporters said. "[The bill] will be able to protect the people engaging in drug checking and the service providers or the harm reduction staff who are doing this work," she said, soon adding, "It's a huge, huge step forward." Green and her colleagues at MADDS hosted a virtual presentation Wednesday to discuss their work testing drug supplies and some of the substances they are detecting at an increasing rate. Xylazine, a veterinary sedative sometimes referred to by users as "tranq," has been present in nearly 40 percent of the opioids MADDS has tested, Green said. It's often found alongside fentanyl, a powerful synthetic opioid that public health officials have said is present in the vast majority of fatal opioid overdoses. Over the past few years, xylazine has not only become more common in the Massachusetts drug supply. Researchers are also finding an increasing ratio of samples that contain more xylazine than fentanyl. Data show that in 2021, about one in five Massachusetts samples had more xylazine than fentanyl. This year, that share is up to more than 28 percent. "We have seen drastic changes in the amount of xylazine. It's quite geographically distinct, so that's an important consideration," Green said. "While we think about statewide, it is really important to know what's happening in your backyard." Front-line drug testers are also finding various synthetic opioids known as nitazenes, which can range in potency from weaker than fentanyl to much stronger. They pose a high risk of overdose, and users can quickly develop a higher tolerance and experience more severe and quicker withdrawal symptoms, MADDS staff said. Another substance detected in Massachusetts illicit drugs is BTMPS, an industrial chemical traditionally used to prevent plastics and other items from degrading when exposed to ultraviolet light. "This is a strange thing to be finding in the drug supply. It has not been found in the drug supply, really, up until now, which, as far as I know, is different -- even xylazine has a long history of it popping up in the drug supply," said Ivy Sabal, a drug checking technician and research assistant with MADDS. That unusual dynamic has stretched across the entire landscape in recent months, according to Green, who pointed to national media coverage about shifts in the drug supply. "A lot of things have been happening recently that have been very odd," Green said. "We're constantly shifting and talking to our colleagues in the region. But since about the summer onwards, we've had a very disrupted drug supply. Some [changes] are concerning. Some are just -- we're not sure what it is and why it's there." Opioid-related overdose deaths in Massachusetts have surpassed 2,000 every year since 2016, though the tally dropped 10 percent from 2022 to 2023, offering a glimmer of hope. The compromise bill that emerged this week aims to further rein in the crisis by boosting access to overdose reversal drugs like naloxone, limiting required reporting about parents on medication to treat opioid use disorder, creating a new licensure and oversight system for recovery coaches, and more. Negotiators dropped one of the most significant, and controversial, ideas that featured in the original Senate bill: safe injection sites. Also known as overdose prevention centers, the facilities allow people to use pre-acquired illegal drugs under the supervision of health care workers, who could intervene to prevent fatal overdoses. Advocates have been pushing lawmakers to embrace the strategy for years, arguing that the sites would prevent unnecessary deaths and keep users alive long enough to seek treatment. DPH announced its support for the sites last year, but House Democrats opted not to embrace the measure amid fears of federal prosecution.