Yes, ratfish are bottom feeders residing at depths of up to 2,000 meters. Crude ratfish liver oil (directly from the liver) does test above the EU limits for contaminants, and it is not advisable to consume it, even for those in Norway who are able to obtain fresh ratfish livers.
Rosita uses a proprietary process that attracts contaminants like a magnet using materials from the ocean. Unlike most fish liver oil producers, who use molecular distillation (high heat) to remove/reduce contaminants, a process that destroys precious vitamins A and D, the Rosita process does not damage the vitamins but keeps them intact just as they are in the ratfish's liver. Once the ratfish oil has passed through the contaminant filter, it tests below the strict EU guidelines. It is important to keep in mind that no fish you eat (nor, for that matter, any beef, chicken, or pork) is completely free of dioxins and contaminants unless it is highly processed, which destroys the nutrients.
This article contains information regarding Rosita Ratfish Liver Oil (RFO).