The overall ratings of three chemicals stocks are down on Portfolio Grader this week. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

This week, Tronox Ltd. (TROX) falls to a D (“sell”), worse than last week’s grade of C (“hold”). Tronox produces and markets titanium dioxide. In Portfolio Grader’s specific subcategories of Earnings Momentum, Earnings Revisions, Equity and Margin Growth, TROX also gets F’s. Trade volume is up 819.8% from the previous week. For more information, get Portfolio Grader’s complete analysis of TROX stock.

The rating of Calgon Carbon Corporation (CCC) declines this week from a C to a D. Calgon Carbon is engaged in products and services for purifying water and air. The stock currently has a trailing PE Ratio of 26.00. To get an in-depth look at CCC, get Portfolio Grader’s complete analysis of CCC stock.

This is a rough week for Rockwood Holdings, Inc. (ROC). The company’s rating falls to D from the previous week’s C. Rockwood Holdings is a global developer, manufacturer and marketer of value-added specialty chemicals and advanced materials used for industrial and commercial purposes. The stock gets F’s in Earnings Growth, Earnings Surprise and Margin Growth. For more information, get Portfolio Grader’s complete analysis of ROC stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.