On a positive note, underwater grasses in some areas grow more than 10 feet deep, suggesting that water clarity restoration is possible. Among all the threats to the Bay, toxic chemicals are the most difficult to measure. Very little is known about their effects, including what effects occur at low levels. Some seemingly harmless chemicals are deadly when mixed together. Others, such as PCBs, dioxins and DDT do damage in extremely small doses.
Many chemicals accumulate over time until they, too, do a great deal of damage.
Regulatory and monitoring systems remain insufficient and the approach of using fewer toxic materials has not been widely adopted. On a positive note, the tonnage of reportable industrial discharges of toxic materials from some industries has declined in the last 15 years. Fifteen represents the inverse of seven times the loading, or one seventh. While nitrogen and phosphorus occur naturally, man has introduced levels so artificially high that the Bay cannot sustain them. By 1989, phosphate in detergents were banned in Maryland, Virginia, Pennsylvania and the District of Columbia, which dramatically reduced the level of phosphates in sewage discharges.